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WILLIAM     GILBERT 

OF    COLCHESTER, 


PHYSICIAN   OF   LONDON, 


ON  THE 


LOADSTONE  AND  MAGNETIC  BODIES, 

AND   ON 

THE  GREAT  MAGNET  THE  EARTH. 

%  NEW  P)iYSIOLOGY. 


DEMONSTRATED  WITH  MANY  ARGUMENTS  AND  EXPERIMENTS. 


"  Elecirica,  quae  attrahunt  eadem  ratione  ut  electricum." 


A  TRANSLATION    BY 

P.    FLEURY    MOTTELAY, 

AUTHOR   OF    "the  CHRONOLOGICAL    HISTORY   OF    ELECTRICITY,    MAGNETISM,    ETC.' 


NEW  YORK : 
JOHN   WILEY   &   SONS, 

53  East  Tenth  Street. 
1893. 


Copyright,  1893, 

BY 

P.   F.  MOTTELAY. 


ESOl 


Robert  Druhmond,  Febbis  Bbos., 

Electrotyper,  Printers, 

444  &  446  Pearl  Street,  326  Pearl  Street, 
New  York.  New  York. 


GVILIELMI  GIL' 

B  E  R  T  I   C  O  L  C  E  ST R E  N- 

SIS,^MEDICI  LONDI- 
N  E  N  S I S, 

D  E  M  A  G  R1E  T  E>  M  A  G  N  E  T  P 

<:lSCiVE  CC>RPbRIBVS,ET  DE  I^AG. 

no  magnete  teJlure  j  Phyfiologia  noua^ 

Ip/mmis  ^  jirgumentiSy  &^p^^ 

rimentis  dcraonflrata* 


L  O  H  D  1 N I 


XCVDEBAT  PetrvLShortiANNO 
MDC. 


TRANSLATOR'S   PREFACE. 


I  FIRST  entered  upon  the  translation  of  this,  the  earliest 
known  published  work  treating  of  both  magnetism  and  elec- 
tricity, in  the  beginning  of  1889.  It  was  then  my  intention  to 
place  it  before  the  public  during  the  year  following,  appreciat- 
ing as  I  did  the  demand  for  an  English  version  which  had  been 
frequently  reiterated  by  scientists  generally  in  this  country,  in 
England,  and  upon  the  Continent  of  Europe.  But  the  atten- 
tion I  was  compelled  to  give,  both  here  and  abroad,  to  the 
preparation  of  my  "  Chronological  History  of  Electricity  and 
Magnetism"  has  unavoidably  delayed  the  publication  of  the 
present  volume. 

The  translation  of  De  Magnete  has  been  a  task  of  no  or- 
dinary difficulty ;  it  has  brought  up  problems  innumerable,  the 
solution  gf  which  has  involved  much  laborious  research — as  the 
result  was  meant  to  be  a  clear  and  competent  presentation  of 
the  author  in  idiomatic  English  and  not  simply  a  substitution  of 
English  words  for  Latin.  Nor  would  I  have  ventured  to  appear 
as  the  English  interpreter  of  the  great  Gilbert,  "  father  of  the 
magnetic  philosophy,"  but  for  the  hearty  encouragement  and 
very  material  aid,  in  translating  and  otherwise,  extended  by 
many  literary  and  scientific  friends,  amongst  whom  must  be 
especially  mentioned  Mr.  Joseph  Fitzgerald,  Mr.  E.  McMillan, 


VI  TRANSLATOR'S  PREFACE. 

Mr.  Joseph  Wetzler,  Dr.  Joseph  V.  Livingston,  Hon.  Park  Ben- 
jamin, and  Prof.  Alfred  M.  Mayer.  I  am  hkevvise  indebted  to 
Prof.  Charles  Sanders  Peirce,  to  Mr.  Latimer  Clark,  F.R.S.,  to 
Dr.  Isaac  H.  Hall,  and  to  Dr.  Charlton  T.  Lewis  for  valuable 
suggestions  as  to  the  general  treatment  of  the  work,  and,  in 
the  words  of  the  celebrated  English  mathematician,  Edward 
Wrip-ht,  I  doubt  not  that  our  united  efforts  "will  find  the 
heartiest  approval  among  all  intelligent  men  and  children  of 
magnetic  science." 

Not  only  does  Gilbert  frequently  make  use  of  what  he 
terms  "  words  new  and  unheard-of,"  besides  attaching  to  many 
others  a  signification  far  different  from  that  generally  recog- 
nized at  this  day,  but,  what  is  worse,  he  retains  to  a  great 
extent  the  terminology  of  the  mediaeval  scholastic  philoso- 
phers. That  terminology  the  translator  must  perforce  retain  ; 
no  substitute  is  possible.  Hence  is  found  a  multitude  of  un- 
couth words  which,  for  the  modern  reader,  require  explanation. 
Of  such  it  is  unnecessary  here  to  make  any  especial  mention, 
since  the  copious  general  index  to  the  present  work  will  indicate 
very  readily  where  they  are  to  be  found.  It  is  known  that  in 
the  philosophy  of  the  schoolmen  (as  in  that  of  Aristotle)  form 
—forma — means  that  which  added  to  matter — inateria — con- 
stitutes the  true  nature  of  the  thing.  Matter /^r  se  is  indiffer- 
ent, indefinite;  form  gives  it  definiteness.  The  earth  is 
informed  With,  verticity — that  is  its  prime  distinction.  When 
any  portion  of  the  earth  loses  verticity  it  loses  its  forma — is 
deformate.  To  restore  to  it  verticity,  is  to  reformate  it,  or  to 
informate  it.  Portions  of  the  earth  that  are  deformate  are,  as 
it  were,  effete,  excrementitious,  waste  matter.  Gilbert  states 
(Book  II,  Chapters  II  and  IV)  that  the  natural  magnetic 
force  (movement)  comes  from  the  prime  forma  of  the  earth,  or 
rather  the  primary  native  strength  {vigor).     Elsewhere  he  tells 


TRANSLATOR'S  PREFACE.  Vll 

US  that  the  earth  and  the  loadstone  conform — conformant — 
magnetic  movements  (Book  II,  Chapter  VI);  and  he  speaks 
of  substances  conformated — confonnatmn — by  the  earth  (Book 
III,  Chapter  IV),  and  of  the  globe  of  earth  as  of  small  account 
and  deformate — deformatum  (Book  V,  Chapter  XII).  He 
speaks  besides  of  the  formate  soul — formata  anima  (Book  V 
Chapter  XII) ;  of  air  or  water  being  informated — informaren- 
tur — by  magnetic  forms  or  spheres  (Book  V,  Chapter  XI);  of 
iron  being  transformated — transformatur  (Book  III,  Chapter 
XII) ;  and  he  adds  that  iron  will  attract  more  properly  if  it  is 
a&ormed—aj^orjnattiin  (Book  II,  Chapter  IV) ;  also  that  if 
will  be  better  if  the  iron's  "acquired  verticity  be,  by  some 
process,  rather  weakened  or  deformated '.' — deformata  (Book 
III,  Chapter  XI). 

England's  great  poet,  John  Dryden,  tells  us  :  "  It  is  almost 
impossible  to  translate  verbally  and  well  at  the  same  time ;  for 
the  Latin  (a  most  severe  and  compendious  language)  often 
expresses  that  in  one  word  which  either  the  barbarity  or  the 
narrowness  of  modern  tongues  cannot  supply  in  more.  .  .  . 
But  since  every  language  is  so  full  of  its  own  proprieties  that 
what  is  beautiful  in  one  is  often  barbarous,  nay,  sometimes 
nonsense,  in  another,  it  would  be  unreasonable  to  limit  a 
translator  to  the  narrow  compass  of  his  author's  words ;  it  is 
enough  if  he  choose  out  some  expression  which  does  not 
vitiate  the  sense."  While,  in  order  to  do  this  acceptably  in 
the  present  instance,  it  has  often  been  found  necessary  to 
adhere  very  closely  (even  literally)  to  the  original  lines,  the 
"candid  reader"  will  naturally  observe  that  greater  satisfaction 
has  been  vouchsafed  where  paraphrasing  has  been  resorted  to 
for  the  better  comprehension,  more  particularly,  of  words  of 
Gilbert's  own  coinage. 

Following  Dryden,  I  have  translated  with  latitude,  keeping 


vm  TRANSLATOR'S  PREFACE. 

in  view  the  author's  sense  more  particularly  than  his  words^ 
and  amplifying  without  altering  the  former.  Nor  have  I,  in 
so  doing,  attempted,  any  more  than  did  Gilbert,  to  impart 
"  into  the  work  any  graces  of  rhetoric,  any  verbal  ornateness." 
Like  him,  I  have  simply  endeavored  to  treat  "knotty  ques- 
tions about  which  little  is  known  in  such  style  and  in  such 
terms  as  are  needed  to  make  what  is  said  clearly  intelligible." 

Such  few  passages  of  De  Magnete  as  I  have  seen  inde- 
pendently translated  elsewhere  will  be  found  reproduced  in 
their  proper  places,  and  wherever  practicable  I  have  followed 
the  approved  plan  adopted  in  my  "  Chronological  History,"  of 
quoting  numerous  authorities  and  inserting  many  extracts 
from  the  writings  of  different  authors  in  support  of  the  original 
matter.  The  extent  to  which  this  has  been  done  is  shown  in 
the  general  index  accompanying  the  present  work. 

I  may  add  that  I  shall  be  under  obligations  to  those  calling 
attention  to  any  errors,  typographical  or  otherwise,  that  may 
be  found  herein,  as  well  as  to  those  whose  helpful  advice  may 
make  improvement  possible  in  future  editions. 

P.  Fleury  Mottelay. 

New  York,  March  lo,  1892. 


BIOGRAPHICAL  MEMOIR. 


William  Gilbert — or  Gilberd/  as  he  wrote  it — was  born  in 
1540  at  Colchester,  County  Essex,  England,''  of  which  borough 
his  father,  Jerome  (Hieron)  Gilberd,  was  recorder — "a  coun- 
cillor of  great  esteem  in  his  profession."  ^  Very  little  that  is 
reliable  appears  concerning  his  early  years,  but  it  is  known 
that  he  passed  through  the  Grammar  School  of  his  native 
place  and  immediately  afterward  (May  1558)  entered  St. 
John's  College,  Cambridge  (whence,  some  say,  he  went  to 
Oxford),'  proceeding  B.A.  1560,  Fellow  1 560-1 561,  M.A. 
1564,   mathematical    examiner    1 565-1 566,    M.D.    1569,    and 

'  "Gilbert  or  Gilberd.  .  .  .  The  latter  is  used  both  in  his  own  epitaph  and 
his  father's;  and  in  the  records  of  the  town  of  Colchester  :  and,  therefore, 
seems  the  truest."  {BiograpMa  Britannica,  London  1757,  Vol.  IV,  page  2202.) 

-  See  the  Map  of  Colchester  at  page  4,  Vol.  I,  Book  I,  of  Philip 
Morant's  "  Hist,  and  Antiq.  of  Essex,"  London  1768;  also,  a  full  description 
of  the  town  at  pages  266-361,  Vol.  I,  of  Thos.  Wright's  "  Hist,  and  Top.  of  the 
County  of  Essex,"  London  1836,  as  well  as  at  pages  286-322,  Vol.  V,  of  "The 
Beauties  of  England  and  Wales,"  by  E.  W.  Brayley  and  John  Britton,  London 
1810. 

2  Dr.  Thomas  Fuller,  "  Hist,  of  the  Worthies  of  England,"  London  1840, 
page  515. 

*  Antony  A.  Wood,  at  pages  737-738,  Vol.  I,  Athena  Oxonienses,  London 
1813,  says  he  was  "educated  at  both  the  Universities  but  whether  in  Oxon. 
first  or  in  Cambridge,  I  cannot  justly  tell  ";  and  Thomas  Wright  ("  Hist,  and 
Top.  of  County  of  Essex,"  1836,  Vol.  I,  page  311)  states  that  "he  studied  some 
time  in  the  Universities  of  Oxford  and  Cambridge." 

ix 


lOGRAPHICAL  MEMOIR. 


being  elected  a  Senior  Fellow  of  St.  John's  during  the  last- 
named  year. 

Immediately  upon  leaving  college  he  travelled  on  the  Con- 
tinent, "  where  probably  he  had  the  degree  of  Doctor  of 
Physic  conferred  upon  him,  for  he  doth  not  appear  to  have 
taken  it  either  at  Oxford  or  Cambridge," '  and  where,  as  well 
as  in  England,  he  is  said  to  have  "practised  as  a  physician 
with  great  success  and  applause."  In  1573,  he  was  elected  a 
Fellow  of  the  Royal  College  of  Physicians,  and  filled  therein 
many  important  offices,  becoming,  in  turn.  Censor  (i 581-1582, 
1584-1587,  1589-1590),  Treasurer  (i 587-1 591,  1 597-1 599),  Con- 
siliarius  (i  597-1 599),  and  President  (1600).  His  skill  had 
already  attracted  the  attention  of  Queen  Elizabeth,  by  whom 
he  was  appointed  her  physician-in-ordinary,  and  who  showed 
him  many  marks  of  her  favor,  besides  settling  upon  him  an 
annual  pension  (said  to  be  the  only  legacy  left  by  her  to  any 
one)  for  the  purpose  of  aiding  him  in  the  prosecution  of  his 
philosophical  studies. 

Gilbert's  removal  to  court  led  to  the  dispersion  of  the 
members  of  a  society  or  college  which,  it  appears,  frequently 
met  at  his  residence  at  Colchester  (see  illustration).  This 
house,  anciently  known  as  "  Lanseles,"  "  Timperley's,"  "  Tym- 
pornell's "  (Old  Taxation),'  was  located  "  on  St.  Peter's  Hill, 
between  Upper  Thames  Street  and  Little  Knight-Rider 
Street." 

The  early  investigations  of  Gilbert  were  centred  almost 
exclusively  upon  chemistry,  he  "  attaining  to  great  exactness 
therein,"  but  this  branch  was  ere  long  made  to  yield  to  the 
study  of  the  phenomena  of  electricity  and  of  magnetism,  the 


1  Philip  Morant,  loc.  cit..  Vol.  I,  Book  II,  page  117.     See,  likewise,  Ree's 
Cyclopzedia,  1819,  Vol.  XVI,  article  "Gilbert." 


BIOGRAPHICAL   MEMOIR.  XI 

latter  of  which  had  practically  lain  dormant  for  two  thousand 
years — since  the  days  of  Thales  and  Theophrastus.  How  well 
he  succeeded  in  generalizing  and  classifying  these  phenomena, 
after  a  patient  and  exhaustive  line  of  experiments,  is  best 
evidenced  by  the  great  work  which  he  published  during  1600 
under  the  title  of  De  Magnete  magneticisque  corporibus,  et  de 


gilbert's  house  at  COLCHESTER. 


magno  magnete  tellure ;  Physiologia  nova,  plurimis  et  argu- 
mentis  et  experimentis  demonstrata.  This  book,  "  full  of  valu- 
able facts  and  experiments  ingeniously  reasoned  on  "  (J.  F.  W. 
Herschel),  upon  which  Gilbert  was  actively  engaged  during  eigh- 
teen years,  is  his  best  claim  to  recognition  as  the  most  distin- 


Xll  BIOGRAPHICAL  MEMOIR. 

guished  man  of  science  in  England  during  the  reign  of  the 
Virgin  Queen. 

"  The  year  1600,"  observes  the  EngHsh  historian  Henry 
Hallam/  "was  the  first  in  which  England  produced  a  remark- 
able work  in  Physical  Science ;  but  this  was  one  sufficient  to 
raise  a  lasting  reputation  for  its  author.  Gilbert,  a  physician, 
in  his  Latin  treatise  on  the  Magnet  not  only  collected  all  the 
knowledge  which  others  had  possessed  on  the  subject,  but 
became  at  once  the  father  of  experimental  philosophy  in  this 
island,  and,  by  a  singular  felicity  and  acuteness  of  genius,  the 
founder  of  theories  v/hich  have  been  revived  after  a  lapse  of 
ages,  and  are  almost  universally  received  into  the  creed  of 
science.  .  .  .  Gilbert  was  one  of  the  earliest  Copernicans,  at 
least  as  to  the  rotation  of  the  earth,  and,  with  his  usual 
sagacity,  inferred,  before  the  invention  of  the  telescope,  that 
there  are  a  multitude  of  fixed  stars  beyond  the  reach  of  our 
vision." 

Gilbert's  book  created  a  powerful  impression  at  the  time, 
especially  among  the  learned  in  other  parts  of  Europe. 
Galileo  expressed  the  highest  admiration  of  the  work  and  of 
its  author,  and,  it  is  said,  pronounced  Gilbert  "great  to  a 
degree  that  is  enviable."  It  was,  indeed,  by  the  perusal  of 
De  Magnete  that  Galileo  was  induced  to  turn  his  mind  to 
magnetism.''  In  his  own  country,  Gilbert  was  scarcely  so 
highly  appreciated ;  even  Bacon,  though  he  praises  Gilbert  as 
a  philosopher,  speaks  with  little  respect  of  his  theory.  After 
awhile  his  speculations  came  to  be  more  esteemed,  though 
perhaps  not  fully  understood;  but  the  great  superiority  of 
Gilbert  over  all  who  had  previously  treated  of  magnetism,  and 


1  "  Introd.  to  the  Litt.  of  Europe  in  the  15th,  i6th,  and  17th  Centuries," 
London  1839,  Vol.  11,  page  463. 

2  Dr.  Munk,  "  Roll  of  the  Roy.  Col.  of  Phys.,"  1878,  page  78. 


BIOGRAPHICAL  MEMOIR.  Xlll 

"the  extent  to  which  he  had  anticipated  by  his  conjectures 
much  of  our  present  knowledge "  has  only  been  perceived 
since  the  study  of  magnetism  has  assumed  something  like  its 
present  systematic  and  comprehensive  character.^ 

While  Dr.  Whewell  observes^  that  "  Gilbert's  work  contains 
all  the  fundamental  facts  of  the  science,  so  fully  examined, 
indeed,  that  even  at  this  day  we  have  little  to  add  to  them,"  Dr. 
Thomas  Thomson  says^  that  De  Magnete  "  is  one  of  the  finest 
examples  of  inductive  philosophy  that  has  ever  been  pre- 
sented to  the  world.  It  is  the  more  remarkable  because  it 
preceded  the  Novum  Organiim  of  Bacon,  in  which  the  in- 
ductive method  of  philosophizing  was  first  explained."  How 
far  Gilbert  was  ahead  of  his  time  is  best  proved  by  the  works 
of  those  who  wrote  on  magnetism  during  the  first  few  decades 
after  his  death.  They  contributed  in  reality  nothing  to  the 
extension  of  this  branch  of  physical  science.  Poggendorff, 
from  whose  '*  Geschichte  der  Physik "  (page  286)  this  is  ex- 
tracted, calls  Gilbert  "  the  Galileo  of  Magnetism."  By  Dr. 
Priestley  he  was  named  "  the  father  of  modern  electricity." 

In  an  article  written  not  long  since,  Mr.  Conrad  W. 
Cooke,  of  London,  notes  the  high  opinion  of  Gilbert's 
work  entertained,  more  particularly,  by  Nathaniel  Carpenter, 
William  Barlowe,  Francis  Bacon,  Galileo,  and  Humboldt,  and 
he  adds :  "  There  is  abundant  testimony  extant  that  this 
*  De  Magnete'  of  Gilbert's  produced  a  profound  sensation, 
not  only  in  this  country  but  throughout  the  then  civilized 
world,  and  it  is  a  singularly  curious  fact  that  the  brilliancy  of 
a  reputation  so  great  and  so  original  should  have  been  allowed 
in  subsequent  generations  to  have  been  lost  sight  of  in  the 

'  Engl.  Cycl.,  Section  "  Biography,"  Vol.  Ill,  page  102. 

*  "  Hist,  of  the  Inductive  Sciences,"  1859,  Vol.  II,  page  217. 

^  "  History  of  the  Royal  Society,"  London  1812. 


XIV  BIOGRAPHICAL  MEMOIR. 

more  blinding  light  of  more  recent  knowledge  and  discoveries, 
and  it  is  equally  remarkable  that  a  book  so  classical  in  its 
nature,  so  remarkable  in   its  originality  and  prescience,   and 
which  was   thought   so    much    of   during   the   periods   which 
immediately  followed  its  publication,  should  never  have  been 
translated  into  English,  or  indeed  into  any  other  language ; 
and  this  is  rendered  still  more  curious  by  the  fact  that  such  a 
translation  was  actually  called  for  at  the  time,  and  the  want  of 
it  was  considered  remarkable  as  far  back  as  the  year  1618  ; 
and  here  it  will  be  interesting  to  quote  from  the  preface  to  a 
scarce  old  book,  '  Magneticall  Advertisements^  written  at  that 
date  by  the  Ven.  William  Barlowe,'  Archdeacon  of  SaHsbury, 
and  a  very  intimate  friend  of  Dr.   Gilbert.      '  Many  of   our 
nation,'  he  says,  'both  Gentlemen   and  others  of   excellent 
witts  and  louers  of  these  knowledges,  not  able  to  read  Doctor 
Gilbert's  booke  in  Latin  haue  bin  (euer  since  the  first  publish- 
ing thereof)   exceeding   desirous   to  haue   it   translated   into 
English,  but  hitherto  no  man  hath  done  it,  neither  (to  my 
knowledge)  as  yet  goeth  about  any  such  matter,  whereof  one 
principall  cause  is  that  there  are  very  few  that  understande  his 
booke,  because  they  haue  not  Load-stones  of  diuers  formes,  but 
especially  round  ones ; '  and  the  author  gives  a  further  supposi- 
tion that  *  a  second  cause  may  be  for  that  there  are  diuers 
wordes  of  art  in  the  whole  course  of  this  booke  proper  to  this 
subject  and  fitt  to  the  explication  of  his  figures  and  diagrammes 


'  Speaking  of  Wm.  Barlowe,  Anthony  A.  Wood  says  :  "  This  was  the 
person  who  had  knowledge  in  the  magnet  20  years  before  Dr.  Will.  Gilbert 
published  his  book  of  that  subject,  and  therefore  by  those  that  knew  him,  he 
was  accounted  superior,  or  at  least  equal  to  that  doctor  for  an  industrious  and 
happy  searcher  and  finder  out  of  many  rare  and  magnetical  secrets."  {Athena 
Oxonienses,  London  1S13,  Vol.  II,  page  375.)  Under  heading  of  Gilbert,  the 
"British  Museum  Catalogue  of  Printed  Books,"  1888,  has  it  that  "Mag. 
Adv."  was  compiled  partly  from  De  Magnete. 


BIOGRAPHICAL  MEMOIR.  XV 

which  cannot  be  understood  but  by  the  helpe  of  the  Mathe- 
maticks,  and  good  trauelling  in  the  Magneticall  practice.'  " 

Dr.  John  Davy  says^  Gilbert's  '*  work  is  worthy  being 
studied,  and  I  am  surprised  that  an  English  edition  (transla- 
tion) of  it  has  never  been  published."  He  also  alludes  to  the 
well-known  reproach  thrown  upon  Gilbert's  philosophy  by 
Francis  Bacon,  who,  in  his  De  Augmentis  Scientiarum,  remarks 
that  "  Gilbert  has  attempted  to  raise  a  general  system  upon 
the  magnet,  endeavoring  to  build  a  ship  out  of  materials  not 
sufficient  to  make  the  rowing-pins  of  a  boat." 

On  the  other  hand,  Digby  and  Barlowe  place  Gilbert  upon 
a  level  with  Harvey,  Galileo,  Gassendi,  and  Descartes,"  while 
the  celebrated  historian  of  the  Council  of  Trent,  Father  Paul 
— Fra  Paolo  Sarpi,— who  will  not  be  thought  an  incompetent 
judge,  names  Gilbert,  with  Francis  Vieta  (the  greatest  French 
mathematician  of  the  sixteenth  century),  as  the  only  original 
writer  among  his  contemporaries.^ 

It  is  deserving  of  notice  that  Gilbert  was  the  first  to  use 
the  terms  **  electric  force,"  "  electric  emanations,"  and  "  electric 
attraction."  He  it  was,  also,  who  gave  the  name  of  "pole" 
to  the  extremities  of  the  magnetic  needle  pointing  to  the 
poles  of  the  earth,  calling  south  pole  the  extremity  that 
pointed  toward  the  north,  and  north  pole  the  extremity  point- 
ing toward  the  south.  In  the  words  of  Sir  David  Brewster, 
Gilbert  applies  the  term  magnetic  to  all  bodies  which  are  acted 
upon  by  loadstones  and  magnets,  in  the  same  manner  as  they 
act  upon  each  other,  and  he  finds  that  all  such  bodies  contain 
iron  in  some  state  or  other.     He  considers  the  phenomena  of 


^  "Memoirs  of  the  Life  of  Sir  H.  Davy,"  London  1836,  Vol.  \,  page  309. 
^  "Nouvelle  Biog.  G6n6rale,"  1858,  Tome  VIII,  page  494. 
'  Lettere  di  Fra  Paolo,  page  31;  Hallam,  "  Introd.  to  Lit.  .  .  .  ",  1839,  Vol. 
II,  page  464. 


XVI  BIOGRAPHICAL  MEMOIR. 

electricity  as  having  a  considerable  resemblance  to  those  of 
magnetism,  though  he  points  out  the  differences  by  which  the 
two  classes  of  phenomena  are  marked. 

To  give  here  such  an  analysis  as  Gilbert's  admirable  work 
merits  would  be  impracticable,  but  the  short  review  of  it  made 
by  Dr.  John  Robison^  deserves  full  reproduction  as  follows : 
"  In  the  introduction,  he  recounts  all  the  knowledge  of  the 
ancients  on  the  subject,  and  their  supine  inattention  to  what 
was  so  entirely  in  their  hands,  and  the  impossibility  of  ever 
adding  to  the  stock  of  useful  knowledge,  so  long  as  men 
imagined  themselves  to  be  philosophising,  while  they  were  only 
repeating  a  few  cant  words  and  the  unmeaning  phrases  of  the 
Aristotelian  school.  It  is  curious  to  mark  the  almost  perfect 
sameness  of  Dr.  Gilbert's  sentiments  and  language  with  those 
of  Lord  Bacon.  They  both  charge,  in  a  peremptory  manner, 
all  those  who  pretend  to  inform  others,  to  give  over  their 
dialectic  labours,  which  are  nothing  but  ringing  changes  on  a 
few  trite  truths,  and  many  unfounded  conjectures,  and  im- 
mediately to  betake  themselves  to  experiment.  He  has 
pursued  this  method  on  the  subject  of  magnetism,  with 
wonderful  ardour,  and  with  equal  genius  and  success  ;  for  Dr. 
Gilbert  was  possessed  both  of  great  ingenuity,  and  a  mind 
fitted  for  general  views  of  things.  The  work  contains  a  pro- 
digious number  and  variety  of  observations  and  experiments, 
collected  with  sagacity  from  the  writings  of  others,  and  insti- 
tuted by  himself  with  considerable  expense  and  labour.  It 
would  indeed  be  a  miracle  if  all  Dr.  Gilbert's  general  infer- 
ences were  just,  or  all  his  experiments  accurate.  It  was  un- 
trodden ground.  But,  on  the  whole,  this  performance  con- 
tains more  real  information  than  any  writing  of  the  age  in 

*  "  System  of  Mechanical  Philosophy,"  London  1822,  page  209. 


BIOGRAPHICAL  MEMOIR.  XVll 

which  he  lived,  and  is  scarcely  exceeded  by  any  that  has  ap- 
peared since.  We  may  hold  it  with  justice  as  the  first-fruits 
of  the  Baconian  or  experimental  philosophy. 

"This  work  of  Dr.  Gilbert's   relates  chiefly  to  the  load- 
stone, and  what  we  call  magnets ;  that  is,  pieces  of  steel  which 
have  acquired  properties  similar  to  those  of   the  loadstone. 
But    he    extends    the    term    magnetism  ^    and    the     epithet 
magnetic,  to  all  bodies  which  are  affected  by  loadstones  and 
magnets,  in  a  manner  similar  to  that  in  which  they  affect  each 
other.      In  the  course  of  his  investigations,  indeed,  he  finds 
that  these  bodies  are  only  such  as  contain  iron  in  some  state 
or  other ;  and  in  proving  this  Hmitation  he  mentions  a  great 
variety  of  phenomena  which  have  a  considerable  resemblance 
to   those   which   he   allows  to  be  magnetical,  namely,  those 
which  he  called  electrical,  because  they  were  produced  in  the 
same  way  that  amber  is  made  to  attract  and  repel  light  bodies. 
He  marks,  with  care,  the  distinctions  between  these  and  the 
characteristic   phenomena  of   magnets.      He  seems  to  have 
known,  that   all   bodies   may  be   made    electrical,  while  fer- 
ruginous substances  alone  can  be  made  magnetical.     It  is  not 
saying  too  much  of  this  work  of  Dr.  Gilbert's  to  affirm,  that  it 
contains  almost  everything  that  we  know  about  magnetism. 
His  unwearied    diligence  in  searching  every  writing  on  the 
subject,  and  in  getting  information  from  navigators,  and  his 
incessant  occupation  in  experiments,  have  left  very  few  facts 
unknown  to  him.     We  meet  with  many  things  in  the  writings 
of  posterior  enquirers,  some  of  them  of  high  reputation,  and 
of  the  present  day,  which  are  published  and  received  as  notable 


*  Humboldt  states  that  in  Gilbert  "  we  do  not  find  either  the  abstract  ex- 
pression electricitas,  or  the  barbarous  word  magnetismus  introduced  in  the 
eighteenth  century."  ("  Cosmos,"  1849,  Vol.  II,  page  726,  note.) 


XVni  BIOGRAPHICAL  MEMOIR. 

discoveries,  but  are  contained  in  the  rich  collection  of  Dr. 
Gilbert.  We  by  no  means  ascribe  all  this  to  mean  plagiarism, 
although  we  know  traders  in  experimental  knowledge  who  are 
not  free  from  this  charge.  We  ascribe  it  to  the  general  in- 
dolence of  mankind,  who  do  not  take  the  trouble  of  consulting 
originals,  where  things  are  mixed  with  others  which  they  do 
not  want,  or  treated  in  a  way,  and  with  a  painful  minuteness, 
which  are  no  longer  in  fashion.  We  earnestly  recommend  it  to 
the  perusal  of  the  curious  reader.  He  will  (besides  the  phi- 
losophy) find  more  facts  in  it  than  in  the  two  large  folios  of 
Scarella." 

The  manner  in  which  "  this  great  man  arrived  to  discover 
so  much  of  magnetical  philosophy  "  and  "  all  the  knowledge 
he  got  on  this  subject,"  we  are  told  by  Sir  Kenelm  Digby,' 
"was  by  forming  a  little  load-stone  into  the  shape  of  the  earth. 
By  which  means  he  compassed  a  wonderful  designe,  which  was, 
to  make  the  whole  globe  of  the  earth  maniable ;  for  he  found 
the  properties  of  the  whole  earth,  in  that  little  body ;  which 
he  therefore  called  a  terrella,  or  little  earth  f  and  which  he 
could  manage  and  try  experiences  upon,  at  his  will.  And  in 
like  manner,  any  man  that  hath  an  aim  to  advance  much  in 
natural  sciences,  must  endeavour  to  draw  the  matter  he  en- 
quireth  of,  into  some  small  modell,  or  into  some  kinde  of 
manageable  method ;  which  he  may  turn  and  wind  as  he 
pleaseth.  And  then  let  him  be  sure,  if  he  hath  a  competent 
understanding,  that  he  will  not  misse  his  mark." 

Amongst  the  many  other  ingenious  contrivances  frequently 
alluded  to  in  his  book,  Gilbert  mentions  the  versorium,  an  iron 
needle  moving  freely  upon  a  point,  with  which  he  was  enabled 


1  "  Treatise  of  Bodies,"  1645,  Chap.  XX,  page  225. 

2  See  De  Magnete,  Book  I,  Chap.  III. 


BIOGRAPHICAL  MEMOIR.  XIX 

to  measure  excited  electricity.  He  is,  besides,  the  inventor  of 
"  two  most  ingenious  and  necessarie  Instruments  for  Sea  men 
to  find  out  thereby  the  latitude  of  any  place  upon  sea  or  land, 
in  the  darkest  night,  that  is  without  the  helpe  of  Sunne,  Moone 
or  Starre."  These  instruments  are  described  in  Thomas  Blun- 
derville's  quarto  work  entitled  "  The  Theoriques  of  the  seuen 
Planets,  shewing  their  diuerse  motions*  .  .  .  printed  at  London 
1602." 

Of  the  monumental  De  Magnete,  Prof.  Robison  states''  that 
he  knew  of  but  two  British  editions  and  that  he  had  "  seen 
five  editions  published  in  Germany  and  Holland  before  1628." 
This  would  make  seven  editions  in  all,  if  the  1600  Amsterdam 
edition — which  Kuhn  alludes  to — be  included.  Sir  John  Leslie, 
however,  says'  that  "  Gilbert's  original  work  was  republished 
at  Ferrara  in  1629,  with  a  commentary  by  Cabaeus."  Thus 
are  eight  distinct  editions  referred  to.     Yet,  but 

Two  editions  (1600,  1633)  are  named  by:  J.  C.  Brunet 
(Londini,  Sedini) ;  J.  C.  Poggendorff^  and  "  Inter- 
national Encycl."*  (London,  Stettin);  "  AUgemeine 
Ency."  ^  and  "  Biographic  Universelle  "  ^  (London, 
Sedan)  ; 
Three  editions  (1600,  1628,  1633)  are  given  by  W.  T. 
Lowndas,'  S.  A.  Allibone,"  J.  G.  T.  Graesse,"  S.  P. 

'  "  Bibliotheca  Britannica,"  Edinburgh  1824,  Vol.  I,  Authors,  by  R.  Watt, 
pages  124  and  414. 

2  "  Edinb.  Cyclop.,"  article  Gilbert.  See  J.  C.  Poggendorff,  "  Geschichte 
der  Physik,"  Leipsig  1879,  page  279. 

3  Fifth  Dissert.  "  Encycl.  Brit.",  page  741. 

^  "Manuel  du  Libraire,"  Paris  1861,  Vol.  II,  page  1592. 

*  "  Biog. -Liter.  Handw.",  Leipsig  1863,  Vol.  I,  page  895. 

^  Vol.  VI,  page  679,  1892  ed.  '  Leipzig  1858,  Sec.  I,  page  229. 

8  Bruxelles  1843-1847,  Vol.  VII,  page  253. 

»  "The  Bibliog.  Manual,"  1859,  Part  IV,  page  890. 

1"  "Critical  Diet,  of  Engl.  Lit.",  1859,  Vol.  I,  page  668. 

"  "Tresor  de  Livres  Rares  et  Precieux,"  1862. 


XX  BIOGRAPHICAL  MEMOIR. 

Thompson'    (Londini,    Sedini) ;    Dr.    J.    Lamont* 
(Londini,  Stettin);   British  Museum   Catalogue  of 
Printed  Books,  London  1888  (Londini,  Sedani); 
Four  editions  are  alluded  to  at  page  201  of  the  (1880) 
Catalogue  of  the  Ronalds  Library,  edited  by  Alfred 
J.    Frost,   viz.,    Londini    1600,    Amsterdam    1600, 
Sedini  1628,  1633  ;  and 
Five  editions  appear  in  Mr.  C.  W.  Cooke's  article'  as  fol- 
lows :  London  1600,  Stettin  1628,  1633,  Franckfort 
1629,  1638,  the  same  being  specified  in  the  "  Ninth 
Britannica,"*  with  the  difference  that  Sedan  takes 
the  place  of  Stettin. 
The  other  editions  cannot  be  traced   through  any  of  the 
numerous  catalogues  of  public  and  private  libraries,  or  in  the 
records  of  prominent  sales  at  auction,  which  have  been  consulted. 
The  above  has  brought  about  the  question  as  to  the  true 
significance  of  Sedini,  with  the  result  following : 

Sedan,  on  the  Meuse,  in  France,  is  given  the  Latin 
name  Sidanum  by  Mr.  Bescherelle,*  also  Sedanum 
in  the  "  Diet.  G6og.  Port.",  1809,  page  617,  as  well 
as  by  Em.  Bowen,^  Henry  Cotton,^  and  M.  Des- 
champs.* 
Stettin,  on  the  Oder,  in  Prussia,  is  called  in  Latin 
Stetinum  ("Diet.  G^og.  Port",  1809,  page  652; 
Em.    Bowen,   loc.    cit.    Vol.    I,   page    701).      See 


*  "  Gilbert  of  Colchester,  an  Eliz.  Magn.",  1891,  pages  43-44. 

2  "  Handb.  des  Magnetismus,"  Leipzig  1867,  page  434. 

3  London  "Engineering"  for  the  month  of  December,  1889. 

*  Volume  X,  page  592. 

5  "Grand  Diet,  de  G6og.  Univ.",  1857,  Tome  IV,  page  560. 
fi  "Compl.  Syst.  of  Geog.",  1747,  Vol.  I,  page  401. 
'  "  Typog.  Gazetteer,"  1825,  page  146. 
8  "Diet,  de  Geog.",  1870,  page  1158. 


BIOGRAPHICAL  MEMOIR.  XXI 

Sedmum — likewise  Sideni,  Sidini,  Sudeni,  in  "  Lexi- 
con Geog.",  1657,  page  361;  "  Diet.  Geog.",  Nice 
1 79 1,  page  308,  "Diet.  Geog.  Univ.",  1832,  pages 
453-454 ;  as  well  as  by  Larousse/  Cotton,*  Des- 
champs/  and  W.  Smith.*  Gilbert  alludes  to  the 
Sudini  of  Prussia,  Book  2,  Chap.  2. 
Sedini,  Sedinu,  Seduni,  Sedunum  (French  Sion,  Ger- 
man Sitten),  were  names  attaching  to  place  and 
people  along  the  banks  of  the  Rhone  in  Switzer- 
land (Phil.  Brietio,  "  Parallela  Geographiae,"  1648, 
Vol.  I,  page  347 ;  Geo.  Long,  "  Atlas  of  Class. 
Geog.'^  1874,  Map  VII ;  A.  G.  Findlay,  "Classical 
Atlas,''  1853,  Map  XIII ;  Alex.  Maclean,  "Diet,  of 
Am.  Geog.",  1773  ;  Deschamps,  loc.cit.  page  1161). 

As  the  French  would  say,  il  y  en  a  un  peu  pour  tous  les  goUts, 
but  since  Wolfgang  Lochman(n),  the  publisher  of  the  editions 
imprinted  Sedini  1628  and  1633,  was  a  resident  of  Stettin 
(J.  C.  Poggendorff,  "  Biogr.-Liter.  Handw.,"  1863,  Vol.  I,  page 
1484),  the  natural  inference  to  be  drawn  is  that  the  imprint 
Sedini  stands  for  Stettin,  and  not  for  Sedan  as  many  have  it. 

In  the  present  volume  will  be  found  photo-lithographic 
reproductions  of  three  of  the  above-named  title-pages.  That 
of  the  1600  Londini  is  taken  from  the  copy  of  Mr.  Charles 
L.  Clarke,  whereto  allusion  is  made  hereafter,  while  the 
1628  Sedini  is  reproduced  from  the  copy  in  the  library 
of  the  English  Institute  of  Electrical  Engineers,  and  the 
1633  Sedini  from  the  copy  belonging  to  Dr.  Park  Benja- 
min  of   New  York   City.     The    1628   is  the   most   elaborate 

'  "Grand  Diet.  Univ.",  1875,  Tome  XIV,  pages  477,  1099. 

'  H.  Cotton,  loc.  cit.  page  152. 

^  Deschamps,  loc.  cit.  pages  1161,  1175. 

*  "Diet,  of  Gr.  and  Rom.  Geog.",  1857,  Vol.  II,  pages  995,  1042. 


XXU  BIOGRAPHICAL  MEMOIR. 

of  all  known  Gilbert  title-pages.  As  described  by  Prof.  Sir 
Wm.  Thomson  (Lord  Kelvin),  it  is  "  in  the  form  of  a  monu- 
ment, ornamented  with  commemorative  illustrations  of  Gil- 
bert's theory  and  experiments,  and  a  fantastic  indication  of 
the  earliest  European  mariner's  compass,  a  floated  loadstone, 
but  floating  in  a  bowl  on  the  sea  and  left  behind  by  the  ship 
sailing  away  from  it !  In  the  upper  left-hand  corner  is  to  be 
seen  Gilbert's  terrella  and  orbis  virtutis^  The  terrella  is  a  lit- 
tle globe  of  loadstone,  which  he  made  to  illustrate  his  idea  that 
the  earth  is  a  great  globular  magnet.  .  .  .  The  orbis  virtutis 
is  simply  Gilbert's  expression  for  what  Faraday  called  the  field 
of  force,  that  is  to  say,  the  space  round  a  magnet,  in  which 
magnetic  force  is  sensibly  exerted  on  another  magnet,  as,  for 
instance,  a  small  needle,  properly  placed  for  the  test.  Gil- 
bert's word  virtue  expresses  even  more  clearly  than  Faraday's 
word  force  the  idea  urged  so  finely  by  Faraday,  and  proved  so 
validly  by  his  magneto-optic  experiment,  that  there  is  a  real 
physical  action  of  a  magnet  through  all  the  space  round  it  tho' 
no  other  magnet  be  there  to  experience  force  and  show  its 
effects."  The  meaning  of  the  Httle  bars  bordering  the  terrella 
is  explained  in  Gilbert's  book  (Lib.  I,  cap.  iii,  and  Lib.  V, 
cap.  ii),  where  he  alludes  to  the  application  of  bits  of  fine  iron 
wire  as  long  as  a  barley-corn,  etc.,  etc. 

After  the  death  of  Queen  Elizabeth,  March  24,  1603,  Gil- 
bert was  continued  in  his  position  as  royal  physician  by  King 
James  I.,  but  he  survived  his  benefactress  only  a  few  months; 
he  died,  some  say  at  Colchester,  others  at  London,  on  the  30th 
November  of  the  same  year.  He  was  buried  in  the  chancel  of 
the  Church  of  the  Holy  Trinity  in  Colchester,  where  a  monu- 


>  See   cuts   of    Orbis   Virtutis  in  De  Magnete,  Book  II,  Chapters  VI  and 
XXVII,  also  Book  V,  Chap,  II. 


BIOGRAPHICAL  MEMOIR.  XXlll 

ment '  was  erected  to  him  by  his  brothers,  who  placed  upon 
it  a  Latin  inscription  ^  which  appears  at  page  79  of  Doctor 
Munk's  "  Roll  of  the  Royal  College  of  Physicians,"  London 
1878.  Dr.  B.  W.  Richardson  has  translated  the  inscription  as 
follows : 

Ambrose  and  William  Gilberd  have  placed  this  tomb  In  memory  of 
brotherly  piety.  To  William  Gilberd,  Senior,  Gentleman,  and  doctor  of 
medicine.  This,  the  eldest  son  of  Jerome  Gilberd,  Gentleman,  was  born 
in  the  town  of  Colchester,  studied  the  art  of  medicine  at  Cambridge, 
practiced  the  same  for  more  than  thirty  years  ai  London,  with  singular 
credit  and  success.  Hence  called  to  Court,  he  was  received  with  highest 
favor  by  Queen  Elizabeth,  to  whom,  and  to  her  successor  James,  he 
served  as  chief  physician.  He  composed  a  book  celebrated  among  for- 
eigners concerning  the  magnet  for  nautical  science.  He  died  in  the 
year  of  the  Human  Redemption  1603,  the  last  day  of  November,  in  the 
63d  year  of  his  age. 

The  inscription  is  thus  rendered  by  Thos.  Wright,  at  pages 
310-31 1,  Vol.  I,  of  his  (London  1836)  '■'■  Hist,  and  Topog.  of  the 
County  of  Essex:" 

Ambrose  and  William  Gilberd  erected  this  monument  to  William 
Gilberd,  senior,  esq.,  and  doctor  of  physic,  in  memory  of  his  fraternal 
affection.  He  was  the  eldest  son  of  Jerom  Gilberd,  Esq.,  born  in  the 
town  of  Colchester,  studied  physic  at  Cambridge,  and  practised  at  Lon- 
don more  than  thirty  years  with  the  greatest  applause,  and  equal  suc- 
cess. And  being  sent  for  to  Court,  he  was  received  into  the  highest 
favor  by  Queen  Elizabeth,  to  whom  as  also  to  her  successor,  James,  he 
was  principal  physician.  He  wrote  a  book  concerning  the  magnet, 
much  celebrated  by  those  engaged  in  nautical  affairs.  He  died  in  the 
year  of  Human  Redemption  1603  on  the  last  day  of  November,  in  the 
63d  year  of  his  age. 

'  An  engraving  of  this  monument  is  given  in  Philip  Morant's  "History 
of  Colchester,"  and  it  is  described  ("  Diet,  of  Nat.  Biog.",  London  1890,  Vol. 
XXI,  page  338)  as  being  "a  panel  surrounded  by  a  frame  of  Jacobean  pattern, 
surmounted  by  pinnacles  bearing  globes  and  14  shields  of  armorial  achieve- 
ments." 

'  "The  epitaph  thereon  is  very  unelegant  and  hardly  latin.  .  .  ."  {Biog. 
Brit.,  London  1757,  Vol.  IV,  page  2203.) 


XXIV  BIOGRAPHICAL  MEMOIR. 

Gilbert  was  never  married.  He  bequeathed  to  the  College 
of  Physicians  "  all  the  books  in  his  library,  his  globes,  instru- 
ments and  cabinets  of  minerals."  These  were,  unfortunately, 
consumed  in  the  great  London  fire  of  1666.  To  the  University 
of  Oxford  he  left  a  portrait  which  he  is  said  to  have  ordered 
made  of  himself  for  the  purpose  and  which  was  "  placed  in 
the  Gallery  over  the  Schools."'  In  this  portrait,  which  is  be- 
lieved to  have  been  destroyed,"  he  appears  standing  in  his 
doctor's  robes  "  holding  in  his  hand  a  globe  inscribed  terrella, 
whilst  over  his  head  is  the  inscription  '  1591,  aetatis  48,'  and,  a 
little  below  his  left  shoulder,  the  words  '  Magneticarum  virtu- 
tum,  primus  indagator  Gilbertus.'  "  ' 

The  reader  is  shown  in  the  frontispiece  a  copy  of  the  only 
portrait  of  Gilbert  known  at  this  day.  It  was  taken  from  Vol. 
II,  page  33,  of  S.  and  E.  Harding's  "  Biographical  Mirrour," 
and  is  said  to  have  been  engraved  by  Clamp  "  from  an  original 
picture  in  the  Bodleian  Library,  Oxford." "  As  will  be  seen,  it 
lacks  the  inscriptions  before  spoken  of  and  represents  Gilbert 
holding  his  hand  upon  an  ordinary  globe.  It  was  the  central 
portion  of  this  picture  which  was  utilized  by  Mr.  Arthur  Ack- 
land  Hunt  for  his  well-known  historical  painting,  representing 
Gilbert  making  an  experimental  demonstration  in  electricity 
before  Queen  Elizabeth. 

Speaking  of  Gilbert,  Dr.  Fuller  writes  :  "  One  saith  of  him 
that   he  was   Stoicall,  but  not  Cynicall,  which  I   understand 


1  "  The  picture  of  this  famous  doctor,  drawn  to  the  life,  is  hanging  in  the 
school-gallery  at  Oyian^' (AthencB  Oxonienses,  by  Anthony  a  Wood  [1st  edi- 
tion, 1691-2],  London  1813,  Vol,  I,  page  738). 

^  Wood  says  "decayed  and  removed."  at  page  96,  Vol.  II,  of  the  1796 
"  Hist,  and  Antiq.  of  the  Univ.  of  Oxford." 

3  Ninth  "Encycl.  Brit.",  article  Gilbert. 

4  Dr.  Munk's  "  Roll  of  the  Roy.  Col.  of  Physicians,"  1878,  page  79;  "  Diet. 
of  Nat.  Biog.",  London  1890,  Vol.  XXI,  page  338. 


BIOGRAPHICAL  MEMOIR.  XXV 

Reserved,  but  not  Morose,  never  married,  purposely  to  be  more 
beneficial  to  his  brethren.  Such  his  Loyalty  to  the  Queen  that, 
as  if  unwilling  to  survive,  he  dyed  in  the  same  year  with  her, 
1603.  His  Stature  was  Tall,  Complexion  Chearful,  an  Happi- 
ness not  ordinary  in  so  hard  a  student  anjd  retired  a  person." 

Besides  Gilbert's  folio  De  Magnete,  there  appeared  at  Am- 
sterdam, in  165 1,  a  quarto  volume  of  316  pages  entitled  De 
Mundo  Nostro  Sublunari  Philosophia  Nova,  which  was  edited, 
some  say  by  his  brother  William  Gilbert  Junior — ^according  to 
others,  by  the  eminent  English  scholar  and  critic  John  Gruter 
— from  two  MSS.  found  in  the  library  of  Sir  Wm.  Boswell, 
Knight.  According  to  Dr.  John  Davy,  "  this  work  of  Gil- 
bert's, which  is  so  little  known,  is  a  very  remarkable  one,  both 
in  style  and  matter ;  and  there  is  a  vigour  and  energy  of  ex- 
pression belonging  to  it  very  suitable  to  its  originality.  Pos- 
sessed of  a  more  minute  and  practical  knowledge  of  natural 
philosophy  than  Bacon,  his  opposition  to  the  philosophy  of  the 
schools  was  more  searching  and  particular,  and  at  the  same 
time  probably  little  less  efficient."  ^  In  the  opinion  of  Prof. 
John  Robison,  De  Mundo  consists  of  an  attempt  to  establish 
a  new  system  of  natural  philosophy  upon  the  ruins  of  the  Aris- 
totelian doctrine.  We  give  an  extract  from  the  work,  in  a 
footnote  to  the  present  translation  of  Gilbert's  De  Magnete, 
Book  VI,  Chap.  VII,  and  are  also  enabled  to  give  a  reproduc- 
tion of  the  165 1  title-page  made  through  the  courtesy  of  Dr. 
Park  Benjamin. 

The  only  known  writing  of  Gilbert  in  English  is  in  the  form 
of  a  letter  dated  14th  Februrary  (?  1602)  which  appears  at  the 
end    of   William    Barlowe's  "  Magneticall   Advertisements   or 


1  "Memoirs  of  the   Life  of   Sir   Humphry  Davy,"  London   1836,  Vol.   I, 
page  311. 


xxvi  BIOGRAPHICAL  MEMOIR. 

divers  observations  concerning  the   loadstone,"  quarto,  Lon- 
don 1616,  and  reads  as  follows  : 

To  the  Worshipfull  my  good  friend,  Mr.  William  Barlowe  at  Easton  by 
Winchester. 
Recommendations  with  many  thanks  for  your  paines  and  courtesies, 
for  your  diligence  and  enquiring,  and  finding  dinars  good  secrets,  I  pray 
proceede  with  double  capping  your  load-stone  you  speake  of,  I  shall  bee 
glad  to  see  you,  as  you  write,  as  any  man,  I  will  haue  any  leisure,  if  it 
were  a  moneth,  to  conferre  with  you,  you  have  shewed  mee  more — and 
brought  more  light  than  any  man  hath  done.  Sir,  I  will  commend  you 
to  my  L.  of  Effingham,  there  is  heere  a  wise  learned  man,  a  Secretary  of 
Venice,  he  came  sent  by  that  State,  and  was  honourably  received  by  her 
Majesty,  he  brought  me  a  lattin  letter  from  a  Gentle-man  of  Venice  that 
is  very  v/ell  learned,  whose  name  is  Johannes  Franciscus  Sagredus,  he 
is  a  great  Magneticall  man,  and  writeth  that  hee  hath  conferred  with 
diners  learned  men  of  Venice  and  with  the  Readers  of  Padua,  and  re- 
porteth  wonderfuU  liking  of  my  booke,  you  shall  haue  a  coppy  of  the 
letter :  Sir,  I  propose  to  adioyne  an  appendix  of  six  or  eight  sheets  of 
paper  to  my  booke  after  a  while,  I  am  in  hand  with  it  of  some  new  in- 
uentions,  and  I  would  haue  some  of  your  experiments,  in  your  name 
and  inuention  put  into  it,  if  you  please,  that  you  may  be  knowen  for  an 
augmenter  of  that  art.  So  for  this  time  in  haste  I  take  my  leaue  the 
xiiyth  of  February. 

Your  very  louing  friend, 

W.  Gilbert. 

His  intention  to  print  the  short  appendix  was  never  car- 
ried into  effect. 

Professor  Silvanus  P.  Thompson  states  ("  Gilbert  of  Col- 
chester .  .  .  ",  London  1891,  page  40)  that  "with  the  exception 
of  a  single  doubtful  inscription,  '  ex  dono  auctoris,'  in  a  single 
copy  of  De  Magnete,  not  a  line  of  his  [Gilbert's]  handwrit- 
ing is  known  to  exist,  unless  his  hand  wrote  the  signature 
'  Ye  President  and  Societie '  at  the  end  of  a  Petition,  preserved 
amongst  the  manuscripts  in  the  British  Museum,  addressed  by 
the  Royal  College  of  Physicians  in  1596  to  the  Lords  of  the 
Privy  Council,  complaining  of  the  exactions  of  the  Lord 
Mayor  and  Aldermen  of  London.     It  is  pretty  certain   that 


BIOGRAPHICAL  MEMOIR.  XXVll 

the  MS.  copy  of  De  Mundo  in  the  British  Museum  is  not  in 
the  author's  handwriting ;  for  in  the  Elzevir  Print  there  is  a 
note  stating  that  the  author's  original  manuscript  was  partly 
in  English."  *  It  is  unfortunate  that  Prof.  Thompson's  atten- 
tion should  not  at  the  time  have  been  called  to  the  fact  that 
Mr.  Bernard  Quaritch's  Rough  List  No.  99,  for  September 
1889,  offered  at  page  80 — No.  747 — a  1600  De  Magnete  **  Pres- 
entation copy  from  the  author,  with  inscription  on  title  Dedit 
Guil.  Gilbertiis  Jo.  Sherwood  propriis  inanibus."  This  copy, 
which  formerly  belonged  to  Mr.  Wm.  Constable,  F.R.S.  and 
F.A.S.,  is  now  the  property  of  Mr.  Chas.  L.  Clarke,  C.E.,  New 
York  City,  through  whose  courtesy  the  reproduction  of  the  title 
bearing  the  inscription  appears  at  page  iii.  A  comparison  of 
the  writing  in  both  inscriptions  would  prove  interesting. 

"  Mahomet's  Tombe  at  Mecha  is  said  strangely  to  hang 
up,  attracted  by  some  invisible  Load-stone,  but  the  memory  of 
the  Doctor  will  never  fall  to  the  ground,  which  his  incompar- 
able Book  De  Magnete  will  support  to  Eternity."  ^ 

In  his  epistle '  to  Dr.  Walter  Charleton  (physician  in  ordi- 
nary to  King  Charles  I.),  the  celebrated  EngHsh  poet,  John 
Dryden,  predicts  that 

"  Gilbert  shall  live  till  loadstones  cease  to  draw, 
Or  British  fleets  the  boundless  ocean  awe." 

'  "  A  copy  in  MS,  among  the  Royal  collection  in  the  British  Museum.  .  ,  . 
It  consists  of  five  books  and  is  written  on  paper."  (Casley's  Catalogue,  page  212.) 
The  work  is  alluded  to  at  page  283  "Les  Elzevier,"  Alph.  Willems,  Bruxelles 
1880,  also  at  page  203  of  Ann.  de  Impr.  Elsevirienne,  Chas.  Pieters,  Gand 
1851. 

^  Dr.  Thomas  Fuller,  "  The  History  of  the  Worthies  of  England,"  London 
1840,  page  515.  See  references  to  Mahomet's  Shrine:  in  Gilbert's  De  Magnete, 
1600,  Book  I,  Chap.  I  ;  in  Porta 's  "Natural  Magick,"  1658,  Book  VII,  Chap. 
XXVII;  in  Sir  Thomas  Brown's  Pseudoloxia,  Epidemica,  1658,  Book  II,  pages 
78-79;  in  Cabaeus,  Philosophia  Magneiica,  1629,  Lib.  IV,  Chap.  XVIII,  page  335. 

*  Epistle  the  Third,  at  page  15,  Vol.  XI,  of  the  Works  of  John  Dryden, 
London  1803. 


CONTENTS. 


PAGE 

Translator's  Preface •  •, v 

Biographical  Memoir ix 

Address  by  Edward  Wright xxxviii 

Author's  Preface , . .       xlvii 

Explanation  of  some  Terms  used  in  this  Work liii 

BOOK  I. 

Chapter  I.  Writings  of  ancient  and  modern  authors  concerning  the  load- 
stone :  various  opinions  and  delusions i  • 

IL  The  loadstone:  what  it  is:  its  discovery 15 

III.  The  loadstone  possesses  parts  differing  in  their  natural  powers, 

and  has  poles   conspicuous  for  their  properties 22 

IV.  Which  pole  is  the  north:  how  the   north  pole  is  distinguished 

from  the  south  pole 26 

V.  One  loadstone  appears  to  attract  another  in  the  natural  posi- 
tion; but  in  the  opposite  position  repels  it  and  brings  it  to 

rights 28 

VI.  The  loadstone  attracts  iron  ore  as  well  as  the  smelted  metal. . .     31 

VII.  What  iron  is;  what  its  matter;  its  use 33 

VIII.  In  what  countries  and  regions  iron  is  produced 43 

IX.  Iron  ore  attracts  iron  ore    46 

X.  Iron  ore  has  and  acquires  poles,  and  arranges  itself  with  refer- 
ence to  the  earth's  poles , ,, 47 

XL  Wrought-iron,  not  magnetized  by  the  loadstone,  attracts  iron.     48 
XII.  A  long  piece  of  iron,  even  not  magnetized,  assumes  a  north 

and  south  direction  50 

XIII.  Smelted  iron  has  in  itself  fixed  north  and  south  parts,  magnetic 

activity,  verticity,  and  fixed  vertices  or  poles 51 

XIV.  Of  other  properties  of  the  loadstone  and  of  its  medicinal  virtue     52 
XV.  The  medicinal  power  of  the  iron 55 

XVI.  That  loadstone  and  iron  ore  are  the  same,  and  that  iron  is  ob- 
tained from  both,  like  other  metals  from  their  ores;  and 
that  all  magnetic  properties  exist,  though  weaker,  both  in 

smelted  iron  and  in  iron  ore 59 

xxxi 


XXXll  CONTENTS. 

PAGE 

XVII.  That  the  terrestrial  globe  is  magnetic  and  is  a  loadstone;  and, 
just  as  in  our  hands  the  loadstone  possesses  all  the  prim- 
ary powers  (forces)  of  the  earth,  so  the  earth  by  reason  of 
the  same  potencies  lies  ever  in  the  same  direction  in  the 
universe 64 

BOOK   II. 

Chapter  I.  Of  magnetic  movements 72 

II.  Of  magnetic  coition,  and,  first,  of  the  attraction  exerted  by 
amber,  or,  more  properly,  the  attachment  of  bodies  to 
amber 74 

III.  Opinions  of  others  concerning  magnetic  coition,  which  they  call 

attraction 97 

IV.  Of  the  strength  of  a  loadstone  and  its  form:  the  cause  of  coition  105 
V.  In  what  manner  the  energy  inheres  in  the  loadstone 115 

VI.  How  magnetized  iron  and  smaller  loadstones  conform  to  the 

terrella,  and  to  the  earth  itself,  and  are  governed  thereby.  121 
VII.  Of  the  potency  of  the  magnetic  force,  and  of  its  spherical  ex- 
tension   123 

VIII.  Of  the  geography  of  the  earth  and  the  terrella 124 

IX.  Of  the  equinoctial  circle  of  earth  and  terrella 126 

X.  The  earth's  magnetic  meridians 126 

XI.  Parallels 127 

XII.  The  magnetic  horizon 128 

XIII.  Of  the  magnetic  axis  and  poles 125 

XIV.  Why  the  coition  is   stronger  at  the  poles  than  in  the  parts  be- 

tween equator  and  pole;  and  the  relative  power  of  coition 

in  different  parts  of  the  earth  and  the  terrella 129' 

XV.  The  magnetic  force  imparted  to  iron  is  more  apparent  in  an 
iron  rod,  than  in  an  iron  sphere,  or  cube,  or  iron  of  any 

other  shape 131 

XVI.  That  motion  is  produced  by  the  magnetic  force  through  solid 

bodies  interposed:  of  the  interposition  of  a  plate  of  iron.   132 
XVII.  Of   the   iron   helmet  (cap)  of   the   loadstone,  wherewith   it   is 
armed  at  the  pole  to  increase  its  energy;  efficiency  of  the 

same 137 

XVIII.  An  armed  loadstone  does  not  endow  with  greater  force  mag- 
netized iron  than  does  an  unarmed  one ,   138 

XIX.  That  unition  is  stronger   with  an  armed   loadstone:  heavier 
weights  are  thus  lifted:  the   coition  is  not  stronger,  but 

commonly  weaker 139 

XX.  That  an  armed  magnet  lifts  another,  and  that  one  a  third:  this 

holds  good  though  there  be  less  energy  in  the  first 139 

XXI.  That  when  paper  or  other  medium  is  interposed,  an  armed  load- 
stone does  not  lift  more  than  one  unarmed 140 


CONTENTS.  XXXlll 

PAGE 

XXII.  That  an  armed  loadstone  does  not  attract  more  than  an  un- 
armed one;  and  that  the  armed  stone  is  more  strongly 
united  to  the  iron,  is  shown  by  means  of  an  armed  load- 
stone and  a  cylinder  of  polished  iron 140 

XXIII.  The  magnetic  force  makes  motion   toward  union,  and  when 

united  connects  firmly 142 

XXIV.  That  iron  within  the  field  of  a  loadstone  hangs  suspended  in  air, 

if  on  account  of  an  obstacle  it  cannot  come  near 143 

XXV.  Intensifying  the  loadstone's  forces 145 

XXVI.  Why  the  love  of  iron  and  loadstone  appears  greater  than  that  of 
loadstone  and  loadstone,  or  iron  and  iron  when   nigh  a 

loadstone  and  within  its  field   148 

XXVII.  That  the  centre  of  the  magnetic  forces  in  the  earth  is  the  centre 

of  the  earth;  and  in  the  terrella  the  terrella's  centre 150 

XXVIII.  That  a  loadstone  does  not  attract  to  a  fixed  point  or  pole  only, 
but  to   every  part  of   a  terrella,   except  the  equinoctial 

circle 151 

XXIX.  Of  difference  of  forces  dependent  on  quantity  or  mass 152 

XXX.  The  shape  and  the  mass  of  an  iron  object  are  important  in 

magnetic  coitions 152 

XXXI.  Of  oblong  and  round  stones 154 

XXXII.  Some  problems  and  magnetic  experiments  on  the  coition,  and 

repulsion,  and  regular  movement  of  magnetic  bodies  ....   155 

XXXIII.  Of  the  difference  in  the  ratio  of  strength  and  movement  of 

coition  within  the  sphere  of  influence 161 

XXXIV.  Why  a  loadstone  is  of  different  power  in  its  poles  as  well  in  the 

north  as  in  the  south  regions 164 

XXXV.  Of  a  perpetual-motion  engine  actuated  by  the  attraction  of  a 

loadstone,  mentioned  by  authors 166 

XXXVI.  How  a  strong  loadstone  may  be  recognized 167 

XXXVII.  Uses  of  the  loadstone  as  it  affects  iron 169 

XXXVIII.  Of  the  attractions  of  other  bodies 170 

XXXIX.  Of  mutually  repellent  bodies 175 

BOOK   III. 

Chapter  I.  Of  direction 177 

II.  Directive  (or  versorial)  force,  which  we  call  verticity:  what  it  is; 
how  it  resides  in  the  loadstone;  and  how  it  is  acquired 

when  not  naturally  produced 183 

III.  How  iron  acquires  verticity  from  the  loadstone,  and  how  this 

verticity  is  lost  or  altered 189 

IV.  Why  magnetized  iron  takes  opposite  verticity:  and  why  iron 
touched  by  the  true  north  side  of  the  stone  moves  to  the 
earth's  north,  and  when  touched  by  the  true  south  side  to 


XXXI V  CONTENTS. 

PAGE 

the  earth's  south:  iron  rubbed  with  the  north  point  of  the 
stone  does  not  turn  to  the  south,  nor  vice  versa,  as  all 

writers  on  the  loadstone  have  erroneously  thought 192 

V.  Of  magnetizing  stones  of  different  shapes 197 

VI.  What  seems  to  be  a  contrary  movement  of  magnetic  bodies  is 

the  regular  tendence  to  union 198 

VI I.  A  determinate  verticity  and  a  directive  power  make  magnetic 
bodies  accord,  and  not  an  attractional  or  a  repulsive  force, 

nor  strong  coition  alone,  or  unition 200 

VIII.  Of  disagreements  between  pieces  of  iron  on  the  same  pole  of 
a  loadstone;  how  they  may  come  together  and  be  con- 
joined    201 

IX.  Directional  figures  showing  the  varieties  of  rotation 204 

X.  Of  the  mutation  of  verticity  and  magnetic  properties,  or  of  the 

alteration  of  the  force  awakened  by  the  loadstone 208 

XI.  Of  friction  of  iron  with  the  mid  parts  of  a  loadstone  between 

the  poles,  and  at  the  equinoctial  circle  of  a  terrella 210 

XII.   How  verticity  exists  in  all  smelted  iron  not  excited  by  the  load- 
stone   211 

XIII.  Why  no  other  bodies  save  the  magnetic  are  imbued  with  ver- 

ticity by  friction  with  a   loadstone;    and  why  no  body 
not  magnetic  can  impart  and  awaken  that  force 217 

XIV.  The  position  of  a  loadstone,  now  above,  anon  beneath,  a  mag- 

netic body  suspended  in  equilibrium,  alters  neither  the 

force  nor  the  verticity  of  the  magnetic  body 219 

XV.  The  poles,  equator,  centre,  are  permanent  and  stable  in  the  un- 
broken loadstone,  when  it  is  reduced  in  size  and  a  part 

taken  away,  they  vary  and  occupy  other  positions 220 

XVI.  If  the  south  part  of  a  loadstone  have  a  part  broken  off,  some- 
what of  power  is  taken  away  from  the  north  part  also.. . .  222 
XVII.  Of  the  use  of  rotary  needles  and  their  advantages;  how  the  di- 
rective iron  rotary  needles  of  sun-dials  and  the  needles  of 
the  mariner's  compass  are  to  be  rubbed  with  loadstone  in 
order  to  acquire  stronger  verticity 223 

BOOK   IV. 

Chapter  I.  Of  variation 229 

II.  That  variation  is  due  to  inequality  among  the  earth's  eleva- 
tions   235 

III.  Variation  is  constant  at  a  given  place 240 

IV.  The  arc  of  variation  does  not  differ  according  to  distance  be- 
tween places 242 

V.  An  island  in   ocean  does  not  alter   in  variation;    neither  do 

mines  of  loadstone 243 


CONTENTS.  XXXV 

PAGE 

VI.  That  variation  and  direction  are  due  to  the  controlling  force  of 
the  earth  and  the  rotatory  magnetic  nature,  not  by  an  at- 
traction or  a  coition  or  by  other  occult  cause 244 

VII.  Why  the  variation  due  to  this  lateral  cause  is  not  greater  than 
hitherto  it  has  been  observed  to  be,  seldom  appearing  to 
amount  to  two  points  of  the  compass,  except  near  the 

poles  , 246 

VIII.  Of  the  construction  of  the  common  mariner's  compass,  and  of 

the  different  compasses  of  various  nations 248 

IX.  Whether  terrestrial  longitude  can  be  found  from  variation  ....  251 
X.  Why  in  various  places  near  the  pole  the  variations  are  much 

ampler  than  in  lower  latitudes 254 

XI.  Cardan's  error  in  seeking  to  determine    the    distance   of  the 
earth's  centre  from  the  centre  of  the  world  by  means  of  the 

loadstone  (in  his  De  Proportionibus,Y) 255 

XII.  Of  finding  the  amount  of  the  variation;  what  the  quantity  is  of 
the  arc  of  the  horizon  from  its  arctic  or  antarctic  intersec- 
tion by  a  meridian  to  the  point  toward  which  the  needle 
turns 256 

XIII.  Observations  made  by  seamen  commonly  vary  and  are  untrust- 

worthy, partly  though  mistakes  and  want  of  knowledge 
and  the  imperfectness  of  the  instruments,  and  partly  be- 
cause the  sea  is  seldom  so  calm  but  shadows  or  lights 
may  rest  on  the  instruments 265 

XIV.  Of  the  variation  under  the  equinoctial  line  and  nearby 267 

XV.  The  variation   of   the    magnetized   needle  in   the   great  sea, 

Ethiopic  and  American,  below  the  equator 267 

XVI.  Of  the  variation  in  Nova  Zembla 269 

XVII.  Variation  in  the  South  Sea 270 

XVIII.  Of  the  variation  in  the  Mediterranean  Sea 270 

XIX.  The  variation  in  the  interior  of  the  great  continents 271 

XX.  The  variation  in  the  Eastern  Ocean 272 

XXI.  How  the  deviation  of  the  needle  is  greater  or  less  according  to 

the  distance  oif  places 273 

BOOK  V. 

Chapter  I.  Of  the  dip  of  the  magnetic  needle -    . ,  275 

II.  Diagram  showing  dip  of  the  magnetic  needle  in  different  posi- 
tions of  a   sphere   and  horizons   of  the  earth  in  which 

there  is  a  variation  of  dip 282 

III.  An  instrument  for  showing  by  the  action  of  a  loadstone  the 
degree  of  dip  below  the  horizon  in  any  latitude.     Descrip- 

tioM  of  the  instrument;  its  uses 285 

IV.  Of  a  suitable  length  of  needle  on  the  terrella  for  showing  the 

dip 288 


XXXVl  CONTENTS. 

TAGS 

V,  That  dip  is  not  caused  by  the  attraction  of  a  loadstone  but  by 

its  power  of  giving  direction  and  rotation 289 

VI.  Of  the  ratio  of  the  dip  to  latitude  and  the  causes  thereof 292 

VII.  Explanation  of  the  diagram  of  the  rotation  of  magnetized  iron.  295 
VIII.  Diagram  of  the  rotation  of  magnetized  iron  showing  the  mag- 
netic dip  in  all  latitudes,  and   showing  the  latitude  from 

the  rotation  and  dip 297 

IX,  Demonstration  of  direction,  or  of  variation  from  the  true  di- 
rection, together  with  dip,  simply  by  the  movement  in 

water,  due  to  the  power  of  controlling  and  rotating 301 

X.  Of  variation  of  dip 303 

XI.  Of  the  formal  magnetic  act  spherically  effused 304 

XII.  The  magnetic  force  is  animate,  or  imitates  a  soul;  in  many  re- 
spects it  surpasses  the  human  soul  while  that  is  united  to 
an  organic  body 308 

BOOK  VI. 

Chapter  I.  Of  the  globe  of  earth  as  a  great  loadstone. 313 

II.  The  magnetic  axis  of  the  earth  remains  invariable 315 

III.  Of  the  daily  magnetic  revolution  of  the  globes,  as  against  the 
time-honored  opinion  of  a  primum  mobile:    a   probable 

hypothesis 3^7 

IV.  That  the  earth  hath  a  circular  motion 327 

V.  Arguments  of  those  who  deny  the  earth's  motion,  and  refuta- 
tion thereof 335 

VI.  Of  the  cause  of  the  definite  time  of  the  total  revolution  of  the 

earth 343 

VII.  Of  the  earth's  primary  magnetic  nature  whereby  her  poles  are 

made  different  from  the  poles  of  the  ecliptic 347 

VIII.  Of  the  precession  of  the  equinoxes  by  reason  of  the  magnetic 

movement  of  the  earth's  poles  in  the  arctic  and  antarctic 

circle  of  the  zodiac. 348 

IX.  Of  the  anomaly  of  the  precession  of  the  equinoxes  and  of  the 

obliquity  of  the  zodiac 35^ 


To  the  most  learned  Mr.  William  Gilbert,  the  distinguished  Lon- 
don physician  and  father  of  the  magnetic  philosophy  :  a 
laudatory  address  concerning  these  books  on  magnetism,  by 
Edward  Wright. 

Should  there  be  any  one,  most  worthy  sir,  who  shall  dis- 
parage these  books  and  researches  of  yours,  and  who  shall 
deem  these  studies  trifling  and  in  no  wise  sufficiently  worthy 
of  a  man  consecrated  to  the  graver  study  of  medicine,  of  a 
surety  he  will  be  esteemed  no  common  simpleton.  For  that 
the  uses  of  the  loadstone  are  very  considerable,  yea  admirable, 
is  too  well  known  even  among  men  of  the  lowest  class  to  call 
for  many  words  from  me  at  this  time  or  for  any  commenda- 
tion. In  truth,  in  my  opinion,  there  is  no  subject-matter  of 
higher  importance  or  of  greater  utility  to  the  human  race 
upon  which  you  could  have  brought  your  philosophical  talents 
to  bear.  For  by  the  God-given  favor  of  this  stone  has  it  come 
about  that  the  things  which  for  so  many  centuries  lay  hid — 
such  vast  continents  of  the  globe,  so  infinite  a  number  of 
countries,  islands,  nations  and  peoples — have  been,  almost 
within  our  own  memory,  easily  discovered  and  oft  explored, 
and  that  the  whole  circle  of  the  globe  has  been  circumnavi- 
gated more  than  once  by  our  own  Drake  and  Cavendish: 
which  fact  I  wish  to  record  for  the  undying  remembrance  of 
those  men.  For,  by  the  showing  of  the  magnetized  needle, 
the  points  North,  South,  East  and  West  and  the  other  points 
of  the  compass  are  known  to  navigators,  even  while  the  sky  is 


XXXVIU  ADDRESS  BY  EDWARD    WRIGHT. 

murky  and  in  the  deepest  night ;  by  this  means  seamen  have 
understood  toward  what  point  they  must  steer  their  course,  a 
thing  that  was  quite  impossible  before  the  wondrous  discovery 
of  the  north-pointing  power  of  the  loadstone.  Hence  sailors 
of  old  were  often  beset,  as  we  learn  from  the  histories,  by  an 
incredible  anxiety  and  by  great  peril,  for,  when  storms  raged 
and  the  sight  of  sun  and  stars  was  cut  off,  they  knew  not 
whither  they  were  sailing,  neither  could  they  by  any  means 
or  by  any  device  find  out.  Hence  what  must  have  been  the 
gladness,  what  the  joy  of  all  mariners  when  first  this  magnetic 
pointer  offered  itself  as  a  most  sure  guide  on  the  route  and  as 
a  God  Mercury !  But  it  was  not  enough  for  this  magnetic 
Mercury  simply  to  point  out  the  way  and,  as  it  were,  to  show 
by  the  extended  finger  whither  the  course  must  be:  it  soon 
began  even  to  indicate  the  distance  of  the  place  whither  the 
voyage  is  made.  For,  since  the  magnetic  pointer  does  not 
always  regard  the  same  northern  spot  in  every  locality,  but 
usually  varies  therefrom,  either  to  the  east  or  to  the  west,  tho' 
it  nevertheless  hath  and  holds  ever  the  same  variation  in  the 
same  place,  wherever  that  may  be ;  it  has  come  about  that  by 
means  of  this  variation  (as  it  is  called)  closely  observed  and 
noted  in  certain  maritime  regions,  together  with  an  observa- 
tion of  the  latitude,  the  same  places  can  afterward  be  found 
by  navigators  when  they  approach  and  come  near  to  the  same 
variation.  Herein  the  Portuguese  in  their  voyages  to  the 
East  Indies  have  the  surest  tokens  of  their  approaching  the 
Cape  of  Good  Hope,  as  is  shown  in  the  narrations  of  Hugo 
Lynschetensis  ^  and  our  very  learned  fellow-countryman  Richard 
Hakluyt ;  hereby,  too,  many  of  our  skilled  British  navi- 
gators when  voyaging  from  the  Gulf  of  Mexico  to  the  Azores, 

*  Jan  Hugo  van  Linscho(o)ten,  Dutch  voyager,  1563-1633, 


ADDRESS  BY  EDWARD    WRIGHT.  XXXIX 

can  tell  when  they  are  come  near  to  these  islands,  though, 
according  to  their  marine  charts,  they  may  appear  to  be  600  Eng- 
lish miles  away.  And  thus,  thanks  to  this  magnetic  indication, 
that  ancient  geographical  problem,  how  to  discover  the  longi- 
tude, would  seem  to  be  on  the  way  to  a  solution ;  for,  the 
variation  of  a  seaboard  place  being  known,  that  place  can  there- 
after be  very  easily  found  as  often  as  occasion  may  require, 
provided  its  latitude  is  not  unknown. 

Yet  somewhat  of  inconvenience  and  difficulty  seems  to  at- 
tach to  this  observation  of  the  variation,  for  it  cannot  be  made 
except  when  the  sun  or  the  stars  are  shining.  Accordingly 
this  magnetic  Mercury  of  the  sea,  better  far  than  Neptune 
himself  or  any  of  the  sea  gods  or  goddesses,  proceeds  still 
further  to  bestow  blessings  on  all  mariners ;  and  not  alone  in 
the  darkness  of  night  and  when  the  sky  is  murky  does  he  show 
the  true  direction,  but  he  seems  even  to  give  the  surest  indica- 
tions of  the  latitude.  For  the  iron  pointer  suspended  freely 
and  with  the  utmost  precision  in  equilibrium  on  its  axis,  and 
then  touched  and  excited  with  a  loadstone,  dips  down  to  a 
fixed  and  definite  point  below  the  horizon  (e.g.  in  the  latitude 
of  London  it  dips  nearly  72  degrees)  and  there  stands.  But 
because  of  the  wonderful  agreement  and  congruency  mani- 
fested in  nearly  all  and  singular  magnetic  experiments,  equally 
in  the  earth  itself  and  in  a  terrella  (i.e.  a  spherical  loadstone),  it 
seems  (to  say  the  least)  highly  probable  and  more  than  prob- 
able that  the  same  pointer  (similarly  stroked  with  a  loadstone) 
will,  at  the  equator,  stand  in  equilibrium  on  the  plane  of  the 
horizon.  Hence,  too,  it  is  highly  probable  that  in  proceeding  a 
very  short  distance  from  south  to  north  (or  vice  versa)  there 
will  be  a  pretty  sensible  change  in  the  dip ;  and  thus  the  dip 
being  carefully  noted  once  and  the  latitude  observed,  the  same 
place  and  the  same  latitude  may  thereafter  be  very  readily 


xl  ADDRESS  BY  ED  WARD    WRIGHT. 

found  by  means  of  a  dip  instrument  even  in  the  darkest  night 
and  in  the  thickest  weather. 

Thus  then,  to  bring  our  discourse  back  again  to  you,  most 
worthy  and  learned  Mr.  Gilbert  (whom  I  gladly  acknowledge  as 
my  master  iii  this  magnetical  philosophy),  if  these  books  of 
yours  on  the  Loadstone  contained  nought  save  this  one  method 
of  finding  the  latitude  from  the  magnetic  dip,  now  first  pub- 
lished by  you,  even  so  our  British  mariners  as  well  as  the 
French,  the  Dutch,  the  Danes,  whenever  they  have  to  enter  the 
British  sea  or  the  strait  of  Gibraltar  from  the  Atlantic  Ocean, 
will  justly  hold  them  worth  no  small  sum  of  gold.*  And  that 
discovery  of  yours,  that  the  entire  globe  is  magnetical,  albeit 
to  many  it  will  seem  to  the  last  degree  paradoxical,  never- 
theless is  buttressed  and  confirmed  by  so  many  and  so  apposite 
experiments  in  Book  II,  Chapter  XXXIV;  Book  III,  Chap- 
ters IV  and  XII ;  and  throughout  nearly  the  whole  of  Book 
V,  that  no  room  is  left  for  doubt  or  contradiction.  I  come 
therefore  to  the  cause  of  magnetic  variation — a  problem  that 
till  now  has  perplexed  the  minds  of  the  learned  ;  but  no  one 
ever  set  forth  a  cause  more  probable  than  the  one  proposed 
now  for  the  first  time  in  these  your  books  on  the  Loadstone. 
The  fact  that  the  magnetic  needle  points  due  north  in  the 
middle  of  the  ocean  and  in  the  heart  of  continents — or  at  least 


1  Hardly  twenty  years  after  the  English  artificer,  Robert  Norman,  had, 
in  1576,  devised  the  inclinatorium,  which  enabled  him  to  determine  the  dip  or 
inclination  of  the  magnetic  needle,  Gilbert  boasted  that,  by  means  of  this  in- 
strument, he  could  ascertain  a  ship's  place  in  dark  starless  nights,  Gilbert 
commends  the  method  as  applicable  aere  caliginoso;  and  Edward  Knight,  the 
English  mathematician,  in  the  introduction  which  he  added  to  his  master's 
great  work,  describes  this  proposal  as  "worth  much  gold."  Having  fallen  into 
the  same  error  with  Gilbert  of  presuming  that  the  isoclinal  lines  coincided  with 
the  geographical  parallel  circles,  and  that  the  magnetic  and  geographical  equa- 
tors were  identical,  he  did  not  perceive  that  the  proposed  method  had  only  a 
local  and  very  limited  application  (Humboldt,  Cosmos,  1849,  Vol.  I,  page  172, 
and  Vol.  H,  page  658). 


ADDRESS  BY  EDWARD    WRIGHT.  xH 

in  the  heart  of  their  more  massive  and  more  elevated  parts — 
while  near  the  coasts  there  is,  afloat  and  ashore,  an  inclination 
of  the  needle  toward  those  more  massive  parts,  just  as  happens 
in  a  terrella  that  is  made  to  resemble  the  earth  globe  in  its 
greater  elevation  at  some  parts  and  shows  that  it  is  weak  or 
decayed  or  otherwise  imperfect  elsewhere :  all  this  makes  ex- 
ceedingly probable  the  theory  that  the  variation  is  nothing 
but  a  deviation  of  the  magnetic  needle  to  those  more  powerful 
and  more  elevated  regions  of  the  globe.  Hence  the  reason  of 
the  irregularity  that  is  seen  in  the  variations  of  the  compass 
is  easily  found  in  the  inequality  and  anomaly  of  those  more 
elevated  parts.  Nor  do  I  doubt  that  all  those  who  have 
imagined  or  accepted  certain  "  respective  points  "  as  well  as 
they  who  speak  of  magnetic  mountains  or  rocks  or  poles,  will 
begin  to  waver  as  soon  as  they  read  these  your  books  on  the 
Loadstone  and  will  of  their  own  accord  come  over  to  your 
opinion. 

As  for  what  you  have  finally  to  say  of  the  circular  motion 
of  the  earth  and  the  terrestrial  poles,  though  many  will  deem 
it  the  merest  theorizing,  still  I  do  not  see  why  it  should  not 
meet  with  indulgence  even  among  those  who  do  not  acknowl- 
edge the  earth's  motion  to  be  spherical,  seeing  that  even  they 
cannot  readily  extricate  themselves  from  the  many  difficulties 
that  result  from  a  diurnal  motion  of  the  whole  heavens.  For, 
first,  it  is  not  reasonable  to  have  that  done  by  many  agents 
which  can  be  done  by  fewer,  or  to  have  the  whole  heavens 
and  all  the  spheres  (if  spheres  there  be)  of  the  planets  and  fixed 
stars  made  to  revolve  for  the  sake  of  the  diurnal  motion,  which 
may  be  accounted  for  by  a  daily  rotation  of  the  earth.  Then, 
which  theory  is  the  more  probable,  that  the  equinoctial  circle 
of  the  earth  may  make  a  rotatary  movement  of  one  quarter  of 
an  EngHsh  mile  (60  miles  being  equal  to  one  degree  on  the 


Xlii  ADDRESS  BY  EDWARD    WRIGHT. 

earth's  equator)  in  one  second  of  time,  i.e.,  in  about  as  much 
time  as  it  takes  to  make  only  one  step  when  one  is  walking 
rapidly;  or  that  the  equator  of  the  primum  mobile  in  the  same 
time,  with  inexpressible  celerity,  makes  5000  miles  and  that  in 
the  twinkling  of  an  eye  it  makes  about  50  English  miles,  sur- 
passing the  velocity  of  a  flash  of  lightning,  if  they  are  in  the 
right  who  most  strenuously  deny  the  earth's  motion  ?  Finally, 
which  is  the  more  probable,  to  suppose  that  this  little  globe 
of  the  earth  has  some  motion,  or  with  mad  license  of  conjec- 
ture to  superpose  three  mighty  starless  spheres,  a  ninth,  a 
tenth,  and  an  eleventh/  upon  the  eighth  sphere  of  the  fixed 
stars,  particularly  when  from  these  books  on  the  Loadstone  and 
the  comparison  of  the  earth  with  the  terrella  it  is  plain  that 
spherical  motion  is  not  so  contrary  to  the  nature  of  the  earth 
as  it  is  commonly  supposed  to  be  ? 

Nor  do  the  passages  quoted  from  Holy  Writ  appear  to  con- 
tradict very  strongly  the  doctrine  of  the  earth's  mobility.  It 
does  not  seem  to  have  been  the  intention  of  Moses  or  the 
prophets  to  promulgate  nice  mathematical  or  physical  distinc- 
tions :  they  rather  adapt  themselves  to  the  understanding  of 
the  common  people  and  to  the  current  fashion  of  speech,  as 
nurses  do  in  dealing  with  babes;  they  do  not  attend  to  unessen- 
tial minutiae.  Thus,  Genesis  i.  16  and  Psalm  cxxxvi.  7,  9,  the 
moon  is  called  a  great  luminary,  because  it  so  appears  to  us, 
though,  to  those  versed  in  astronomy,  it  is  known  that  very 
many  stars,  fixed  and  planetary,  are  far  larger.  So,  too,  from 
Ps.  civ.  5,^^  no  argument  of  any  weight  can,  I  think,  be  drawn 
to  contradict  the  earth's  mobility,  albeit  it  is  said  that  God  es- 
tablished the  earth  on  her  foundations  to  the  end  it  should  never 

1  See  note,  Book  VI,  Chap.  III. 

*  Psalm  civ.  5,  "  Who  laid  the  foundations  of  the  earth,  that  it  should  not 
be  removed  forever." 


ADDRESS  BY  EDWARD    WRIGHT.  xliii 

be  moved ;  for  the  earth  may  remain  forevermore  in  its  own 
place  and  in  the  selfsame  place,  in  such  manner  that  it  shall  not 
be  moved  away  by  any  stray  force  of  transference,  nor  carried 
beyond  its  abiding  place  wherein  it  was  established  in  the 
beginning  by  the  divine  architect.  We,  therefore,  while  we 
devoutly  acknowledge  and  adore  the  inscrutable  wisdom  of  the 
triune  Godhead,  having  with  all  diligence  investigated  and  dis- 
cerned the  wondrous  work  of  his  hands  in  the  magnetic  move- 
ments, do  hold  it  to  be  entirely  probable,  on  the  ground  of 
experiments  and  philosophical  reasons  not  few,  that  the  earth 
while  it  rests  on  its  centre  as  its  basis  and  foundation,  hath  a 
spherical  motion  nevertheless. 

But,  apart  from  these  matters  (touching  which  no  one,  I  do 
believe,  ever  gave  more  certain  demonstrations),  no  doubt  your 
discussion  if  the  causes  of  variation  and  of  the  dip  of  the  needle 
beneath  the  horizon  (to  say  nothing  of  sundry  other  points 
which  'twould  take  too  long  to  mention)  will  find  the  heartiest 
approval  among  all  intelligent  men  and  "  children  of  magnetic 
science  "  (to  use  the  language  of  the  chemists).  Nor  have  I  any 
doubt  that,  by  publishing  these  your  books  on  the  Loadstone, 
you  will  stimulate  all  wide-awake  navigators  to  give  not  less 
study  to  observation  of  dip  than  of  variation.  For  it  is  highly 
probable,  if  not  certain,  that  latitude,  or  rather  the  effect  of  lati- 
tude, can  be  determined  much  more  accurately  (even  when  the 
sky  is  darkest)  from  the  dip  alone,  than  longitude  or  the  effect 
of  longitude  can  be  found  from  the  variation  even  in  the  full 
light  of  day  or  while  all  the  stars  are  shining,  and  with  the  help 
of  the  most  skilfully  and  ingeniously  contrived  instrument. 
Nor  is  there  any  doubt  that  those  most  learned  men,  Petrus 
Plantius'  (a  most  diligent  student  not  so  much  of  geography  as 

^  Peter  Plancius,  Dutch  theologian  and  astronomer,  1 552-1622. 


xliv  ADDRESS  BY  EDWARD    WRIGHT, 

of  magnetic  observations)  and  Simon  Stevinius/  a  most  eminent 
mathematician,  will  be  not  a  little  rejoiced  when  first  they  set 
eyes  on  these  your  books  and  therein  see  their  own  \i}xvev- 
periKTiv  or  method  of  finding  ports  so  greatly  and  unexpect- 
edly enlarged  and  developed  ;  and  of  course  they  will,  as  far  as 
they  may  be  able,  induce  all  navigators  among  their  own  coun- 
trymen to  note  the  dip  no  less  than  the  variation  of  the 
needle. 

Let  your  magnetic  Philosophy,  most  learned  Mr.  Gilbert,  go 
forth  then  under  the  best  auspices — that  work  held  back  not 
for  nine  years  only,  according  to  Horace's  Counsel,  but  for 
almost  other  nine ;  that  Philosophy  which  by  your  multitudi- 
nous labors,  studies,  vigils,  and  by  your  skill  and  at  your  no 
inconsiderable  expense  has  been  after  long  years  at  last,  by 
means  of  countless  ingenious  experiments,  taken  bodily  out  of 
the  darkness  and  dense  murkiness  with  which  it  was  surrounded 
by  the  speculations  of  incompetent  and  shallow  philosophizers  ; 
nor  did  you  in  the  mean  time  overlook,  but  did  diligently  read 
and  digest  whatever  had  been  published  in  the  writings  whether 
of  the  ancients  or  the  moderns.  Let  it  not  be  afraid  to  face 
the  prejudiced  censure  of  any  supercilious  and  dastardly  phi- 
losophaster  who,  by  enviously  faulting  another's  work  or  by 
fraudulently  taking  the  credit  to  himself,  strives  to  win  a  most 
unsubstantial  renown  ;  for 

Ingenium  magni  livor  detrectat  Homeri, 

(Envy  detracts  from  the  genius  of  mighty  Homer; 

2  Simon  Stevin — Stevinus — celebrated  Flemish  mathematician  (1548-1628), 
published  in  1586  his  well-known  work  on  statics  and  hydrostatics,  in  the  pref- 
ace of  which  he  endeavors  to  prove  that  the  Dutch  language  is  more  ancient 
than  any  other.  This  work  was  soon  followed  by  others,  including  his  De  Motu 
Cceli,  and,  in  1599,  by  his  Dutch  treatise  on  navigation,  translated  in  Latin  by 
Grotius  and  published  in  Leyden.  See  references  made  at  page  486  of  the 
Ronalds  Library  Catalogue,  likewise  note  Book  Iv,  Chap.  IX,  of  the  present 
work. 


ADDRESS  BY  EDWARD    WRIGHT.  xlv 

but 

Quisquis  es,  ex  illo,  Zoile,  nomen  habes. 
whoever  thou  art,  from  him,  Zoilus,  dost  thou  derive  thy  fame.)* 

Your  work,  I  say,  that  has  been  kept  back  for  so  many 

years,  your  New  Physiology  of  the  Loadstone  and  of  the  Great 

Magnet  (i.e.  the  Earth) — a  philosophy  never  to  be  sufficiently 

admired ;  let  it  go  forth  into  the  light  of  publicity ;  for,  believe 

me, 

Siquid  Jiabent  veri  vatum  prcesagia, 

(If  the  presages  of  poets  have  aught  of  truth)* 

these  your  books  on  the  Loadstone  {De  Magnete)  will  do  more 
to  perpetuate  your  memory  than  would  the  monument  of  any 
Magnate  {Magnatis  cujusvis)  erected  over  your  grave. 

*  Ovid's  Remedia  Amoris,  Bohn,  London  1852,  page  475,  tr.  of  Mr.  Henry 
T.  Riley,  who  adds:  It  was  unknown  of  what  parentage  and  country  Zoilus 
was.  He  compiled  a  work  in  dispraise  of  Homer,  and  was  called  by  the 
ancients  '  Homeromastix,'  'the  scourge  of  Homer. 

2  "The  Metamorphoses  of  Ovid,"  XV,  878  (tr,  by  Mr.  Henry  T.  Riley), 
Bohn,  London  1851,  page  553. 


AUTHOR'S   PREFACE. 


TO   THE   CANDID    READER,  STUDIOUS   OF   THE 
MAGNETIC   PHILOSOPHY. 

Since  in  the  discovery  of  secret  things  and  in  the  investi- 
gation of  hidden  causes,  stronger  reasons  are  obtained  from  sure 
experiments  and  demonstrated  arguments  than  from  probable 
conjectures  and  the  opinions  of  philosophical  speculators  of 
the  common  sort ;  therefore  to  the  end  that  the  noble  sub- 
stance of  that  great  loadstone,  our  common  mother  (the  earth), 
still  quite  unknown,  and  also  the  forces  extraordinary  and  ex- 
alted of  this  globe  may  the  better  be  understood,  we  have 
decided  first  to  begin  with  the  common  stony  and  ferruginous 
matter,  and  magnetic  bodies,  and  the  parts  of  the  earth  that 
we  may  handle  and  may  perceive  with  the  senses ;  then  to  pro- 
ceed with  plain  magnetic  experiments,  and  to  penetrate  to 
the  inner  parts  of  the  earth.  For  after  we  had,  in  order  to  dis- 
cover the  true  substance  of  the  earth,  seen  and  examined  very 
many  rriatters  taken  out  of  lofty  mountains,  or  the  depths  of 
seas,  or  deepest  caverns,  or  hidden  mines,  we  gave  much  atten- 

xlvii 


xlviii  AUTHOR'S  PREFACE. 

tion  for  a  long  time  to  the  study  of  magnetic  forces — won- 
drous forces  they,  surpassing  the  powers  of  all  other  bodies 
around  us,  though  the  virtues  of  all  things  dug  out  of  the 
earth  were  to  be  brought  together.  Nor  did  we  find  this  our 
labor  vain  or  fruitless,  for  every  day,  in  our  experiments,  novel, 
unheard-of  properties  came  to  light :  and  our  Philosophy  be- 
came so  widened,  as  a  result  of  diligent  research,  that  we  have 
attempted  to  set  forth,  according  to  magnetic  principles,  the 
inner  constitution  of  the  globe  and  its  genuine  substance,  and 
in  true  demonstrations  and  in  experiments  that  appeal  plainly 
to  the  senses,  as  though  we  were  pointing  with  the  finger,  to 
exhibit  to  mankind  Earth,  mother  of  all. 

And  even  as  geometry  rises  from  certain  slight  and  readily 
understood  foundations  to  the  highest  and  most  difficult 
demonstrations,  whereby  the  ingenious  mind  ascends  above 
the  aether  :  so  does  our  magnetic  doctrine  and  science  in  due 
order  first  show  forth  certain  facts  of  less  rare  occurrence ; 
from  these  proceed  facts  of  a  more  extraordinary  kind  ;  at 
length,  in  a  sort  of  series,  are  revealed  things  most  secret  and 
privy  in  the  earth,  and  the  causes  are  recognized  of  things  that, 
in  the  ignorance  of  those  of  old  or  through  the  heedlessness  of 
the  moderns,  were  unnoticed  or  disregarded.  But  why  should  I, 
in  so  vast  an  ocean  of  books  whereby  the  minds  of  the  studious 
are  bemuddled  and  vexed ;  of  books  of  the  more  stupid  sort 
whereby  the  common  herd  and  fellows  without  a  spark  of 
talent  are  made  intoxicated,  crazy,  puffed  up ;  are  led  to  write 
numerous  books  and  to  profess  themselves  philosophers,  phy- 
sicians, mathematicians,  and  astrologers,  the  while  ignoring  and 
contemning  men  of  learning :  why,  I  say,  should  I  add  aught 
further  to  this  confused  world  of  writings,  or  why  should  I  sub- 
mit this  noble  and  (as  comprising  many  things  before  unheard 
of)  this  new  and  inadmissible  philosophy  to  the  judgment  of 


AUTHOR'S  PREFACE.  xHx 

men  who  have  taken  oath  to  follow  the  opinions  of  others,  to 
the  most  senseless  corrupters  of  the  arts,  to  lettered  clowns, 
grammatists,  sophists,  spouters,  and  the  wrong-headed  rabble, 
to  be  denounced,  torn  to  tatters  and  heaped  with  contumely. 
To  you  alone,  true  philosophers,  ingenuous  minds,  who  not 
only  in  books  but  in  things  themselves  look  for  knowledge, 
have  I  dedicated  these  foundations  of  magnetic  science — a  new 
style  of  philosophizing.  But  if  any  see  fit  not  to  agree  with 
the  opinions  here  expressed  and  not  to  accept  certain  of  my 
paradoxes ;  still  let  them  note  the  great  multitude  of  experi- 
ments and  discoveries — these  it  is  chiefly  that  cause  all  philoso- 
phy to  flourish ;  and  we  have  dug  them  up  and  demonstrated 
them  with  much  pains  and  sleepless  nights  and  great  money  ex- 
pense. Enjoy  them  you,  and,  if  ye  can,  employ  them  for  better 
purposes.  I  know  how  hard  it  is  to  impart  the  air  of  newness  to 
what  is  old,  trimness  to  what  is  gone  out  of  fashion ;  to  lighten 
what  is  dark ;  to  make  that  grateful  which  excites  disgust ;  to 
win  belief  for  things  doubtful ;  but  far  more  difificult  is  it  to 
win  any  standing  for  or  to  establish  doctrines  that  are  novel, 
unheard-of,  and  opposed  to  everybody's  opinions.  We  care 
naught,  for  that,  as  we  have  held  that  philosophy  is  for 
the  few. 

We  have  set  over  against  our  discoveries  and  experiments 
larger  and  smaller  asterisks  according  to  their  importance  and 
their  subtility.  Let  whosoever  would  make  the  same  experi- 
ments, handle  the  bodies  carefully,  skilfully  and  deftly,  not 
heedlessly  and  bunglingly  ;  when  an  experiment  fails,  let  him 
not  in  his  ignorance  condemn  our  discoveries,  for  there  is  naught 
in  these  Books  that  has  not  been  investigated  and  again  and 
again  done  and  repeated  under  our  eyes.  Many  things  in  our 
reasonings  and  our  hypotheses  will  perhaps  seem  hard  to 
accept,  being  at  variance  with  the  general  opinion  ;  but  I  have 


1  AUTHOR'S  PREFACE. 

no  doubt  that  hereafter  they  will  win  authoritativeness  from 
the  demonstrations  themselves.  Hence  the  more  advanced 
one  is  in  the  science  of  the  loadstone,  the  more  trust  he  has  in 
the  hypotheses,  and  the  greater  the  progress  he  makes ;  nor 
will  one  reach  anything  like  certitude  in  the  magnetic  philoso- 
phy, unless  all  or  at  all  events  most  of  its  principles  are  known 
to  him. 

This  natural  philosophy  {^physiologid)  is  almost  a  new  thing, 
unheard-of  before  ;  a  very  few  writers  have  simply  published 
some  meagre  accounts  of  certain  magnetic  forces.  Therefore 
we  do  not  at  all  quote  the  ancients  and  the  Greeks  as  our 
supporters,  for  neither  can  paltry  Greek  argumentation  demon- 
strate the  truth  more  subtilly  nor  Greek  terms  more  effectively, 
nor  can  both  elucidate  it  better.  Our  doctrine  of  the  loadstone 
is  contradictory  of  most  of  the  principles  and  axioms  of  the 
Greeks.  Nor  have  we  brought  into  this  work  any  graces  of 
rhetoric,  any  verbal  ornateness,  but  have  aimed  simply  at 
treating  knotty  questions  about  which  little  is  known  in  such  a 
style  and  in  such  terms  as  are  needed  to  make  what  is  said 
clearly  intelligible.  Therefore  we  sometimes  employ  words 
new  and  unheard-of,  not  (as  alchemists  are  wont  to  do)  in 
order  to  veil  things  with  a  pedantic  terminology  and  to  make 
them  dark  and  obscure,  but  in  order  that  hidden  things  which 
have  no  name  and  that  have  never  come  into  notice,  may  be 
plainly  and  fully  published. 

After  the  magnetic  experiments  and  the  account  of  the 
homogenic  parts  of  the  earth,  we  proceed  to  a  consideration  of 
the  general  nature  of  the  whole  earth ;  and  here  we  decided  to 
philosophize  freely,  as  freely,  as  in  the  past,  the  Egyptians, 
Greeks,  and  Latins  published  their  dogmas;  for  very  many  of 
their  errors  have  been  handed  down  from  author  to  author 
till  our  own  time ;  and  as  our  sciolists  still  take  their  stand  on 


AUTHOR'S  PREFACE.  H 

these  foundations,  they  continue  to  stray  about,  so  to  speak, 
in  perpetual  darkness.  To  those  men  of  early  times  and,  as  it 
were,  first  parents  of  philosophy,  to  Aristotle,  Theophrastus, 
Ptolemaeus,  Hippocrates,  Galen,  be  due  honor  rendered  ever, 
for  from  them  has  knowledge  descended  to  those  that  have 
come  after  them  :  but  our  age  has  discovered  and  brought  to 
light  very  many  things  which  they  too,  were  they  among  the 
living,  would  cheerfully  adopt.  Wherefore  we  have  had  no 
hesitation  in  setting  forth  in  hypotheses  that  are  provable,  the 
things  that  we  have  through  a  long  experience  discovered. 
Farewell.^ 

1  See  the  rendering  of  this  Preface  by  Dr.  B.  W.  Richardson  and  Mr. 
James  Menzies,  which  appeared  in  " The  Asclepiad  "  under  the  title  of  "The 
first  electrician,  William  Gilbert,  M.D." 


EXPLANATION  OF  SOME  TERMS  USED  IN  THIS 

WORK. 

Terrella.     A  spherical  loadstone  or  natural  magnet.' 

Verticity.'^  Polar  strength — activity  (or  what  in  Gilbert's  day  was  under- 
stood as  energy) ;  not  gyrating,  vertiginous,  but  turning  power  :  nor 
is  it  polar  revolution,  but  a  directing  virtue,  an  innate  turning  vigor 
{virtus  convertens).  ^'  * 

Electrics.     Bodies  that  attract  in  the  same  way  as  amber. 

Excited  magnetic  body.  One  (such  as  iron  or  steel)  that  acquires  mag- 
netism from  a  loadstone  or  natural  magnet. 

Magnetized  versorium.  An  iron  bar  or  needle  resting  on  a  point 
(electroscope^)  and  put  in  motion — excited — by  the  loadstone  or 
natural  magnet. 

Non-magnetized  versorium  (the  electroscope  itself).  Made  of  any 
metal,  for  use  in  electrical  experiments. 

Armed  loadstone.     One  that  is  furnished  with  an  iron  helmet  or  cap.* 

Meridionally.     In  the  direction  of  a  meridian. 

Paralleletically.     In  the  direction  of  a  parallel  of  latitude. 

Cuspis  (point).     The  end  of  a  magnetized  versorium. 

'  See  Kenelm  Digby's  allusion  to  terrella  in  the  Biographical  Memoir,  also 
De  Magnete,  Book  I,  Chap,  III. 

^  See  De  Magnete,  Book  I,  Chap.  X. 

2  See  De  Magnete,  Book  II,  Chap.  VI,  also  Prof,  Sir  Wm.  Thomson's  allu- 
sion to  the  orbis  virtutis  in  the  Biographical  Memoir. 

*  "Therefore  true  it  is,  and  conformable  by  every  experiment,  that  Steel 
and  good  Iron  never  excited  by  the  Load-stone,  discover  in  themselves  a  ver- 
ticity;  that  is,  a  directive  or  polary  facultie  whereby,  conveniently  placed,  they 
do  septentrionate  at  one  extream,  and  Australize  at  another  "  (Thomas  Brown, 
Pseudoloxia  Efidemica,  1658,  Book  II,  Chapter  II,  page  63). 

^  Humboldt  says  ("Cosmos,"  1849,  Vol.  II,  page  726)  that  Gilbert  meas- 
ured the  strength  of  excited  electricity  by  means  of  a  small  needle  "not  made 
of  iron  .  .  .  ."  De  Magnete  states  that  the  versorium  was  made  of  any  metal 
{ex  quouis  metallo)  (Verborum,  eighth  line,  and  Book  II,  Chap.  II,  page  48), 
and  alludes  (Book  III,  Chap.  I,  page  115)  to  the  construction  of  a  versorium 
of  two  pieces  of  curved  iron  {ex  duobus  ctirvis  ferramentis). 

«  See  De  Magnete,  Book  II,  Chap.  XVII. 

liii 


liv         EXPLANATION   OF  SOME    OF    THE    TERMS    USED. 

Crotch.  Name  sometimes  given  to  the  end  not  touched  and  excited, 
although  in  some  instruments  both  ends  are  commonly  so  desig- 
nated, according  as  they  are  most  convenient  for  excitation  by  the 
loadstone.^ 

Cork.     Bark  of  the  cork-tree, 

Radius  (of  a  loadstone's  sphere).  A  right  line  drawn  in  the  shortest 
way  from  the  surface  of  a  spherical  loadstone  to  the  surface  of  a 
body,  and  which  when  produced  passes  through  the  centre  of  the 
loadstone. 

Sphere  of  iiifiuence.  The  entire  space  over  which  the  force  of  a  load- 
stone extends.'^ 

Sphere  of  coition.  The  entire  space  over  which  the  smallest  magnetic 
body  moves  toward  a  loadstone. 

Ostensio.     Physical  demonstration  (opposed  to  theory). 

Magnetic  coition.^  This  phrase  is  used  rather  than  attraction  because 
magnetic  movements  do  not  result  from  attraction  of  one  body 
alone  but  from  the  coming  together  of  two  bodies  harmoniously 
(not  the  drawing  of  one  by  the  other) — '^Ojj.odpourf,  the  coition  is 
always  vigorous,  even  though  heavy  substances  make  opposition. 

Declinatorium.  A  bar  or  needle  movable  vertically  on  its  axis  and 
that  is  excited  with  a  loadstone  ;  used  in  the  dip  instrument. 

»  See  De  Magnete,  Book  II,  Chap.  XXXII. 

2  See  note  3,  page  xxxi. 

^  See  De  Magnete,  Book  II,  Chap.  I,  et  seq. 


WILLIAM  GILBERT. 


BOOK   FIRST. 


CHAPTER  I. 

WRITINGS  OF  ANCIENT  AND   MODERN   AUTHORS   CONCERNING 
THE  LOADSTONE  :   VARIOUS   OPINIONS  AND  DELUSIONS. 

In  former  times  when  philosophy,  still  rude  and  uncul- 
tured, was  involved  in  the  murkiness  of  errors  and  ignorances, 
a  few  of  the  virtues  and  properties  of  things  were,  it  is  true, 
known  and  understood  :  in  the  world  of  plants  and  herbs  all  was 
confusion,  mining  was  undeveloped,  and  mineralogy  neglected. 
But  when,  by  the  genius  and  labors  of  many  workers,  certain 
things  needful  for  man's  use  and  welfare  were  brought  to  light 
and  made  known  to  others  (reason  and  experience  meanwhile 
adding  a  larger  hope),  then  did  mankind  begin  to  search  the 
forests,  the  plains,  the  mountains  and  precipices,  the  seas  and 
the  depths  of  the  waters,  and  the  inmost  bowels  of  earth,  and  to 
investigate  all  things.  And  by  good  luck  at  last  the  loadstone 
was  found,  as  seems  probable,  by  iron-smelters  or  by  miners  in 
veins  of  iron  ore.     On  being  treated  by  the  metallurgists,  it 


2  WILLIAM  GILBERT. 

quickly  exhibited  that  strong  powerful  attraction  of  iron — no  la- 
tent nor  obscure  property,  but  one  easily  seen  of  all;  one  observed 
and  commended  with  many  praises.  And  after  it  had  come  forth 
as  it  were  out  of  darkness  and  out  of  deep  dungeons  and  been 
honored  of  men  on  account  of  its  strong  and  marvellous  attrac- 
tion of  iron,  then  many  ancient  philosophers  and  physicians 
discoursed  of  it,  and  briefly  (but  briefly  only)  made  it  matter 
of  record:  as,  for  instance,  Plato  in  the  lo,  Aristotle  only  in 
his  first  book  De  Anima;  likewise  Theophrastus  the  Lesbian, 
Dioscorides,  Caius  Plinius  secundus,  Julius  Solinus.  These 
record  only  that  the  loadstone  attracts  iron  :  its  other  proper- 
ties were  all  hid.  But  lest  the  story  of  the  loadstone  should 
be  jejune  and  too  brief,  to  this  one  sole  property  then  known 
were  appended  certain  figments  and  falsehoods  which  in  the 
early  time  no  less  than  nowadays  were  by  precocious  sciolists 
and  copyists  dealt  out  to  mankind  to  be  swallowed.  For  ex- 
ample, they  asserted  that  a  loadstone  rubbed  with  garlic  does 
not  attract  iron  ;  nor  when  it  is  in  presence  of  a  diamond.' 
The  like  of  this  is  found  in  Pliny  and  in  Ptolemy's  Quadripar- 
titum;  and  errors  have  steadily  been  spread  abroad  and  been 

'  "  As  to  what  some  writers  have  related,  that  a  load-stone  will  not  attract 
iron  if  there  be  a  diamond  near  (Pliny,  Book  XXXVII, Chap.  IV)  and  that  onions 
and  garlic  will  make  it  lose  its  vertue;  these  are  contradicted  by  a  thousand  ex- 
periments which  I  have  tried.  For  I  have  shown  that  this  stone  will  attract  iron 
through  the  very  thickest  diamonds  and  through  a  great  many  thick  skins  which 
an  onion  is  made  up  of  (Rohault's  '  Syst.  Nat.  Phil.,'  1728,  Vol.  II,  page  186). 
That  garlic  does  not  hinder  the  action  of  the  load-stone  is  likewise  shown  by 
Porta,  '  Nat.  Magick,'  1658,  Book  VII,  Chap.  XLVIII,  and  by  Sir  Thos.  Brown, 
at  page  74  of  his  Pseudoloxia  Epidemica  published  in  the  same  year,  but  the 
contrary  is  shown  by  Sir  Hugh  Plat  in  The  Jewell  House  of  Arte  and  Nature, 
originally  published  in  1594."  Consult,  also,  Plutarch,  Quasi.  Conviv.  Lib.  II, 
Qusest  7) ;  Barthol.  de  Glanvil,  Zz^^.  de  Prop.,  Lyons  1480,  folio,  Lib.  XVI; 
Pietro  d'Abano  {Conciliator  Differentiarum,  LI,  Venice  ed.  1526);  Ibn  Roschd's 
Comment,  on  Aristotle,  1550,  T.  4,  p.  143  t. ;  Nic.  de  Cusa,  Opera,  Basilae  1565, 
p.  175  ;  Cardan,  De  Subtil.,  Lib.  VII,  Op.  T.  Ill,  Basilae  ed.  1582  ;  Porta, 
"  Nat.  Magick,"  1658,  Book  VII,  Chap.  LV,  page  215. 


ANCIENT  AND  MODERN  A  UTHORS  ON  THE  LOADSTONE.      3 

accepted — even  as  evil  and  noxious  plants  ever  have  the  most 
luxuriant  growth — down  to  our  day,  being  propagated  in  the 
writings  of  many  authors  who,  to  the  end  that  their  volumes 
might  grow  to  the  desired  bulk,  do  write  and  copy  all  sorts 
about  ever  so  many  things  of  which  they  know  naught  for  cer- 
tain in  the  light  of  experience.  Such  fables  about  the  loadstone 
even  Georgius  Agricola,  a  man  that  has  deserved  well  indeed 
of  letters,  has  inserted  as  truthful  history  in  his  books  De 
Natura  Fossilium,  putting  his  trust  in  others'  writings.*  Ga- 
len, in  the  ninth  book  of  his  De  Simplicium  Medicamentorum, 
Facultatibus,  recognizes  its  medicinal  virtue,  and  its  natural 
power  of  attracting  iron,  in  the  first  book  of  his  De  Naturalibus 
Facultatibus ;  but  he  knew  not  the  cause,  any  more  than 
Dioscorides  before  him,  nor  did  he  seek  further.  But  his 
translator  Matthiolus  furbishes  again  the  garlic  and  diamond 
story,  and  further  brings  in  the  fable  of  Mahomet's  shrine  hav- 
ing an  arched  roof  of  magnets  so  that  the  people  might  be 
fooled  by  the  trick  of  the  cofifin  suspended  in  air,  as  though 
'twere  some  divine  miracle.  But  this  is  shown  to  be  false  by 
the  reports  of  travellers.  Pliny,  however,  records  that  the 
architect  Chinocrates  began  to  put  an  arched  roof  of  load- 
stone on  the  temple  of  Arsinoe  at  Alexandria,  so  that  her 
effigy  in  iron  might  seem  to  be  suspended  in  air:  in  the 
meantime  the  architect  died,  as  also  Ptolemy,  who  had  or- 
dered the  work  to  be  done  in  honor  of  his  sister.*     But  little 

1  See  account  of  the  life  and  writings  of  George  Agricola  in  the  sixth 
chapter  of  "The  History  of  Chemistry,"  by  Dr.  Thomas  Thomson,  who  calls 
him  one  of  the  most  extraordinary  men  as  well  as  one  of  the  greatest  promoters 
of  chemistry  that  have  ever  existed,  and  who  pronounces  Agricola's  De  Re 
Metallica  as,  beyond  comparison,  the  most  valuable  chemical  work  which  the 
sixteenth  century  produced. 

'•^  "  So  it  is  reported  by  Ruffinus,  that  in  the  Temple  of  Serapis  there  was  an 
iron  chariot  suspended  by  Loadstones  in  the  ayr;  which  stones  removed,  the 
chariot  fell  and  dashed  into  pieces.    The  like  doth  Beda  report  of  Bellerophon's 


4  WILLIAM  GILBERT. 

has  been  written  by  the  ancients  about  the  causes  of  the 
attraction  of  iron  :  some  trifling  remarks  of  Lucretius  and 
others  are  extant ;  other  authors  barely  make  slight  mention 
of  the  attraction  of  iron :  all  these  are  berated  by  Cardan  for 
being  so  heedless  and  indifferent  about  so  notable  a  matter, 
$>o  broad  a  field  of  philosophizing,  and  for  not  giving  a  fuller 
account  or  a  more  developed  philosophy  ;  yet  Cardan  himself 
in  his  ponderous  volumes  has  handed  down  to  posterity,  be- 
yond a  few  commonplaces  and  quotations  from  other  writers 
and  false  discoveries,  naught  that  is  worthy  of  a  philosopher.' 
Of  later  authors,  some  tell  only  of  its  efificacy  in  medicine,  as 
Antonius  Musa  Brasevolus,  Baptista  Montanus,  Amatus  Lu- 
sitanus,  as  did  before  them  Oribasius  in  book  13th  of  the  De 
Facultate  Metallicorum,  Avicenna,  Serapio  Mauritanus,  Abo- 
hali  (Hali  Abbas),  Santes  de  Ardoniis,  Petrus  Apponensis, 
Marcellus,  Arnaldus.  Only  a  few  points  touching  the  load- 
stone are  very  briefly  mentioned  by  Marbodeus  Callus, 
Albertus,  Matthseus  Silvaticus,  Hermolaus  Barbatus,  Camillus 
Leonhardus,  Cornelius  Agrippa,  Fallopius,  Joannes  Langius, 
Cardinal  de  Cusa,  Hannibal  Roserius  Calaber :  by  all  these 
the  subject  is  handled  in  the  most  careless  way,  while  they 
repeat  only  the  figments  and  ravings  of  others.  Matthiolus 
compares  the  attractive  virtues  of  the  loadstone,  which  pass 
through  iron,  to  the  mischief  of  the  torpedo,  whose   poison 


horse,  which,  framed  of  iron,  was  placed  between  two  Loadstones,  with  wings 
expansed,  pendulous  in  the  ayr  "  (Thom.  Brown,  Pseudoloxia  Epidemica,  1658, 
Book  II,  page  79).  Consult :  Ath.  Kircheri,  Magnes;  Sive  dearte  magnetica,  1643, 
Lib.  II,  Pars  IV,  Problema  VI;  Vincentii  Burgundi  Spec.  Mai.,  T.  i,  L.  VIII, 
C.  34,  Douai  ed.  1624  ;  Alb.  Magnus,  De  Mineralibus,  LIT,  Tr.  Ill,  c.  vi,  p. 
243,  Lione  165 1  ;  Ausonio  L.  Ampelius,  Lib,  Memorialis,  c.  viii,  Paris  1827  ; 
J.  H.  Martin,  "  Observ.  et  Theories  .  .  .,"  Rome,  1865,  pp.  5,  6,  7. 

^  For  a  better  list  than  Cardan's,  of  authors  who  have  written  on  the  load- 
stone, consult  "Petri  Peregrini  .  .  .  Achillem  T.  Gasserum  .  .  .  Augs- 
burg! .  .  .  1558."  ■^■■'^ 


ANCIENT  AND  MODERN  AUTHORS  ON  THE  LOADSTONE.      5 

passes  through  bodies  and  spreads  in  an  occult  way.  Guliel- 
mus  Puteanus  in  his  Ratio  Purgantiutn  Medicamentorum  dis- 
cusses the  loadstone  briefly  and  crudely.  Thomas  Erastus, 
knowing  naught  of  the  nature  of  the  loadstone,  draws  from 
it  weak;  arguments  against  Paracelsus.  Georgius  Agricola, 
like  Encelius  and  other  writers  on  metals,  simply  describes  it. 
Alexander  Aphrodiseus,  in  his  Problemata,  judges  the  question 
of  the  loadstone  to  be  incapable  of  explication.  Lucretius 
Carus,  the  Epicurean  poet,  deems  the  attraction  to  be  due  to 
this,  that  as  there  is  from  all  things  an  efflux  of  minutest 
bodies,  so  there  is  from  iron  efflux  of  atoms  into  the  space 
betwixt  the  iron  and  the  loadstone — a  space  emptied  of  air 
by  the  loadstone's  atoms  (seeds)  ;  and  when  these  begin  to 
return  to  the  loadstone,  the  iron  follows,  the  corpuscles  being 
entangled  with  each  other.  Something  similar  is  said  by 
Joannes  Costaeus,  following  Plutarch.  Thomas  Aquinas,  in  his 
Fhysica,  Bk.  7,  treating  briefly  of  the  loadstone,  gets  at  the  na- 
ture of  it  fairly  well :  with  his  godlike  and  perspicacious  mind 
he  would  have  developed  many  a  point  had  he  been  acquainted 
with  magnetic  experiments.  Plato  holds  the  magnetic  virtue 
to  be  divine.  But  when,  some  three  or  four  hundred  years  ago, 
the  magnetic  movement  to  the  north  and  the  south  was  discov- 
ered or  recognized  anew,  many  learned  men,  each  according 
to  his  own  gifts,  strove  to  honor  with  admiration  and  praise  or 
to  explain  with  feeble  reasonings  a  property  so  curious  and  so 
necessary  for  the  use  of  mankind.  Of  more  recent  authors, 
very  many  have  striven  to  discover  the  cause  of  this  direction 
and  movement  to  north  and  south,  and  to  understand  this  so 
great  miracle  of  nature  and  lay  it  open  to  others :  but  they 
wasted  oil  and  labor,  because,  not  being  practical  in  the  re- 
search of  objects  in  nature,  being  acquaint  only  with  books, 
being  led  astray  by  certain  erroneous  physical  systems,  and 


O  WILLIAM  GILBERT. 

having  made  no  magnetical  experiments,  they  constructed 
certain  raciocinations  on  a  basis  of  mere  opinions,  and  old- 
womanishly  dreamt  the  things  that  were  not.  Marcilius 
Ficinus  chews  the  cud  of  ancient  opinions,  and  to  give  the 
reason  of  the  magnetic  direction  seeks  its  cause  in  the  constel- 
lation Ursa :  in  the  loadstone,  says  he,  the  potency  of  Ursa 
prevails  and  hence  it  is  transferred  into  the  iron.  Paracelsus 
declares  that  there  are  stars  which,  gifted  with  the  loadstone's 
power,  do  attract  to  themselves  iron.  Levinus  Lemnius  de- 
scribes and  praises  the  mariner's  compass,  and  on  certain 
grounds  infers  its  antiquity;  he  does  not  divulge  the  hidden 
miracle  which  he  makes  profession  to  know.  The  people  of 
Melfi,  in  the  kingdom  of  Naples,  first,  'tis  said,  constructed  a 
mariner's  compass ;  and,  as  Flavius  Blondus  says,  the  towns- 
men do  not  without  reason  boast,  they  were  so  taught  by  one 
Joannes  Goia,  a  fellow-citizen,  in  the  year  1300.'  This  town 
is  in  the  Kingdom  of  Naples,  not  far  from  Salerno,  and  near 
the  promontory  of  Minerva.  The  sovereignty  of  the  place 
was  conferred  by  Charles  V.  on  Andrea  Doria,  the  great  naval 
commander,  in  recognition  of  his  splendid  achievements. 
And  that  nothing  ever  has  been  contrived  by  the  art  of  man 
nor  anything  been  of  greater  advantage  to  the  human  race 
than  the  mariner's  compass  is  certain :  but  many  infer  from 
ancient  writings  and  from  certain  arguments  and  conjectures, 
that  the  compass  was  discovered  earlier  and  received  among 
the  arts  of  navigation.     Knowledge  of  the  mariner's  compass 


*  In  his  "Essay  on  Several  Important  Subjects,"  London  1676,  Joseph 
Glanvill  remarks  (page  33):  "  I  think  there  is  more  acknowledgement  due  to  the 
name  of  this  obscure  fellow,  that  hath  scarce  any  left,  than  to  a  thousand  Alex- 
anders and  Caesars,  or  to  ten  times  the  number  of  Aristotles  and  Aquinas. 
And  he  really  did  more  for  the  increase  of  knowledge,  and  advantage  of  the 
world,  by  this  one  experiment,  than  the  numerous  subtile  disputers  that  have 
lived  ever  since  the  Erection  of  the  School  of  Wrangling." 


ANCIENT  AND  MODERN  A  UTHORS  ON  THE  LOADSTONE.      7 

appears  to  have  been  brought  into  Italy  by  the  Venetian 
Paolo  [Paulum  Veftetum — Marco  Polo]  who  about  the  year 
1260  learned  the  art  of  the  compass  in  China/  still  I  do  not 
want  to  strip  the  Melfitani  of  so  great  an  honor,  seeing  that  by 
them  compasses  were  first  commonly  made  in  Mediterranean 
lands.  Goropius  ascribes  the  invention  to  the  Cimbri  or  Teu- 
tons, on  the  ground  that  the  thirty-two  names  of  the  winds 
inscribed  on  the  compass  are  pronounced  in  German  by  all 
mariners,  whether  they  be  British  or  Spaniards,  or  French- 
men. But  the  Italians  give  them  names  in  their  own  ver- 
nacular. Some  think  that  Solomon,  King  of  Judea,  was 
acquaint  with  the  compass  and  taught  the  use  of  it  to  his 
pilots  for  their  long  voyages  when  they  brought  from  the 
Western  Indies  such  a  quantity  of  gold  :  hence  Arias  Monta- 
nus  holds  that  the  regions  in  Peru  that  abound  in  gold  got 
their  name  from  the  Hebrew  word  Paruaim.  But  it  is  more 
probable  that  the  gold  came  from  the  coast  of  lower  Ethiopia, 
or,  as  others  declare,  from  the  region  called  Cephala.  The 
story  seems  less  true  for  the  reason  that  the  Phcenicians,  next 
neighbors  of  Judea,  most   skilful  navigators   in   early   times 

^  It  appears  to  be  a  remarkable  fact  that  Gilbert,  the  earliest  classical 
writer  on  terrestrial  magnetism,  who  cannot  be  supposed  to  have  had  the 
slightest  knowledge  of  Chinese  literature,  should  regard  the  mariner's  compass 
as  a  Chinese  invention,  which  had  been  brought  to  Europe  by  Marco  Polo. 
The  idea  of  the  introduction  of  the  compass  by  the  last  named,  whose  travels 
occurred  in  the  interval  between  1271  and  1295,  and  who,  therefore,  returned 
to  Italy  after  the  mariner's  compass  had  been  mentioned  as  a  long-known  in- 
strument by  Guyot  de  Provins  in  his  politico-satirical  poem  ("La  Bible,"  1190), 
as  well  as  by  Jacques  de  Vitry  ("  Historise  Hierosolimitanae,"  Cap.  89),  and 
Dante  ("  Paradiso,"  Cant.  XII),  is  not  supported  by  any  evidence.  Before 
Marco  Polo  set  out  on  his  travels  in  the  middle  of  the  thirteenth  century, 
Catalans  and  Basques  already  made  use  of  the  compass  (Humboldt,  "Cosmos," 
Vol.  II,  pages  625,  656;  Raymond  Lully,  in  his  "  De  Contemplatione," 
"  Fenix  de  las  maravillas  del  orbe,"  and  "  Arte  de  Naveguar;"  Azuni,  "  Bous' 
sole,"  page  69;  Miller,  "  History  Philos.  111.",  London  1849,  Vol.  I,  pages  179- 
180). 


8  WILLIAM   GILBERT. 

(whose  talents,  labor,  and  counsels  Solomon  employed  in 
building  ships  and  in  his  expeditions  as  well  as  in  other  ways), 
were  ignorant  of  magnetic  aids,  of  the  use  of  the  mariner's 
compass :  for  were  it  used  by  them,  doubtless  the  Greeks,  the 
Italians,  and  all  the  Barbarians  would  have  known  of  a  thing 
so  necessary  and  so  celebrated  through  common  use ;  nor 
would  things  famous,  most  easily  known,  and  of  the  highest 
necessity,  ever  perish  in  oblivion  ;  on  the  contrary,  the  knowl- 
edge would  have  been  handed  on  to  posterity,  or  some  memo- 
rial in  writing  would  survive. 

Sebastian  Cabot  first  discovered  that  the  magnetized  iron 
(needle)  varied/  Gonzales  Oviedo  first  made  mention  in  his 
history  that  in  the  meridian  of  the  Azores  there  is  no  varia- 
tion. [Jean  Frangois]  Fernel,  in  his  book  De  Abditis  Rerum 
CausiSf  says  that  in  the  loadstone  is  a  hidden  and  abstruse 
cause  :  elsewhere  he  says  this  cause  is  celestial  ;  and  he  does 
but  explain  the  unknown  by  the  more  unknown.  This  search 
after  hidden  causes  is  something  ignorant,  beggarly,  and  re- 
sultless.  The  ingenious  Fracastorio,  a  philosopher  of  no  com- 
mon   stamp,''    asks  what    gives    direction    to    the    loadstone 

^  At  page  150  of  the  1869  London  edition  of  Mr.  J.  F.  Nicholls'  Life  of 
Seb.  Cabot,  it  is  said  the  latter  represented' to  the  King  of  England  that  the 
variation  of  the  compass  was  different  in  many  places,  and  was  not  absolutely- 
regulated  by  distance  from  any  particular  meridian;  also,  that  he  could  point  to 
a  spot  of  no  variation,  and  that  those  whom  he  trained  as  seamen,  as  Chancel- 
lor and  Stephen  Burrough  were  particularly  attentive  to  this  problem,  noting  it 
at  one  time  thrice  within  a  short  space  ("  Biddle,"  Memoir  of  Sebastian  Cabot, 
1831;  Humboldt,  in  both  his  "  Examen  Critique"  and  his  "Cosmos,"  treating 
of  "Oceanic  Discoveries"). 

'^  Hieronymus  Fracastorio,  the  great  cotemporary  of  Columbus,  to  whom 
Gilbert  alludes  so  frequently,  was  one  of  the  most  learned  men  of  his  time 
(1483-1553).  From  his  early  youth,  he  devoted  himself  to  the  study  of  the 
sciences,  medicine  especially,  and  he  is  said  to  have  been  made  professor  of 
logic  at  the  University  of  Padua  when  only  nineteen  years  of  age.  The  first 
edition  of  his  complete  works  appeared  at  Venice  in  1555.  Edward  Biot  tells  us 
that  it  was  Fracastorio  and  Peter  Appian,  who  first  made  generally  known  in 


ANCIENT  AND  MODERN  A  UTHORS  ON  THE  LOADSTONE.      9 

[needle],  and  imagines  the  existence  of  hyperborean  magnetic 
mountains,  attracting  objects  of  magnetic  iron.  This  opinion, 
in  some  degree  accepted  by  others  also,  many  authors  follow 
in  their  writings,  their  geographical  maps,  their  marine  charts, 
and  their  descriptions  of  the  globe :  dreaming  [imagining  to 
themselves  the  existence  of]  magnetic  poles  and  mighty  cliffs, 
apart  from  the  earth's  poles.  Of  date  two  hundred  years  or 
more  earlier  than  Fracastorio,  is  a  small  work  attributed  to  one 
Petrus  Peregrinus,  a  pretty  erudite  book  considering  the  time  : 
many  believe  it  owes  its  origin  to  the  opinions  of  Roger 
Bacon,  Englishman  of  Oxford.'  In  this  work  the  arguments 
touching  the  magnetic  direction  are  drawn  from  the  celestial 
poles  and  from  the  heaven  itself.  From  this  book  of  Petrus 
Peregrinus,  Joannes  Taisner  Hannonius"  extracted  the  matter 

Europe  the  peculiar  fact,  noticed  by  the  Chinese  astronomers  as  early  as  837, 
that  the  tails  of  comets  are  always  turned  away  from  the  sun,  so  that  their  line 
of  prolongation  passes  through  its  centre  (Humboldt,  "Cosmos,"  1849,  Vol,  I, 
page  86,  and  Vol.  II,  page  697). 

1  Roger  Bacon,  sometimes  called  Friar  Bacon,  flourished  after  the  dis- 
tinguished Albertus  Magnus  (who,  strangely  enough,  is  omitted  by  Olaus  Bor- 
richius  in  his  list  of  alchymistical  writers),  and  was  by  far  the  most  illustrious 
and  best  informed  of  all  the  alchymists.  In  one  of  his  numerous  works  he 
dwells  upon  the  mariner's  compass  as  a  miraculum  in  parte  notum.  Alexander 
von  Humboldt  remarked  that  Roger  Bacon,  Albertus  Magnus,  as  well  as  the 
Arabian  philosophers  Avicenna  and  Averroes,  passed  for  the  representatives  of 
all  the  knowledge  of  their  time. 

2  Joannes  Taisner  of  Ath  in  Hainault  (hence  Hannonius)  is  mentioned 
(Ronald's  Catalogue,  page  493)  as  the  author  of  "...De  Natura  Magnetis  et 
ejus  effectibus  .  .  .  ,"Coloniae  1562,  an  English  translation  of  which,  by  Richarde 
Eden,  was  published  in  London  about  1579.  The  first  Gasser's  printed  edition 
of  Petrus  Peregrinus  is  dated  Augsburg  1558.  To  Peregrinus  is  ascribed  the  first 
mention  of  the  double  polarity  of  the  magnet  (Nicolas  Cabeo,  T/ziL  Magnetica, 
Ferrara  1629,  Lib.  II,  C.  3,  8),  as  well  as  the  designation  of  the  word  poles  for 
points  of  greatest  energy  in  the  magnet  (Bertelli  Barnabita,  "  Sopra  P.  Pere- 
grino  .  .  . ,"  Roma  1868,  pp.  34,  62,  63,  70,  71).  As  is  already  known,  the  last 
claim  has  by  others  been  made  for  Gilbert.  Taisner's  De  Natura,  again  alluded 
to  by  Gilbert  (Book  Il.Chap.XXXV),  is  said  by  Bertelir  and  others  to  be  a  more 
manifest  plagiarism  upon  Peregrinus  than  even  that  of  Antonius  Fantis  of 
Treviso.     (Nic.  Cabeo,  Phil.  Magn.,  1629,  page  23.) 


lO  WILLIAM  GILBERT. 

of  a  little  volume,  which  he  published  for  new.  Cardan  makes 
much  of  the  star  in  the  tail  of  Ursa  Major  ;  the  cause  of  varia- 
tion he  assigns  to  its  rising,  thinking  that  variation  is  always 
certain  at  the  rising  of  the  star.  But  the  difference  of  varia- 
tion for  change  of  locality,  and  the  mutations  in  many  places 
— mutations  that  even  in  the  southern  regions  are  irregular — 
preclude  this  exclusive  dominance  of  one  star  at  its  northern 
rising.  The  College  of  Coimbra  seeks  the  cause  in  some 
region  of  the  heavens  nigh  to  the  pole  ;  Scaliger,  in  the  131st 
of  his  -Exercitationes  on  Cardan's  work  De  Subtilitate,  brings  in 
a  celestial  cause  to  himself  unknown,  and  terrestrial  loadstones 
that  have  nowhere  been  discovered  ;  and  seeks  the  cause  not 
in  the  "  siderite  mountains  "  but  in  that  force  which  formed 
them,  to  wit,  in  the  part  of  the  heavens  which  overhangs  that 
northern  point.  This  opinion  the  learned  author  dresses  in 
abundant  verbiage  and  crowns  with  many  subtile  observations 
in  the  margin  :  but  his  reasons  are  not  so  subtile.  Martinus 
Cortesius  holds  that  the  seat  of  the  attraction  is  beyond  the 
poles,  and  that  it  is  the  heavens  in  motion.  One  Bessard,  a 
Frenchman,  studies  the  pole  of  the  Zodiac,  but  to  as  little  pur- 
pose. Jacobus  Severtius,  of  Paris,  after  quoting  a  few  obser- 
vations of  others,  fashions  new  errors  about  loadstones  of  dif- 
ferent regions  being  different  in  direction,  as  also  about  the 
eastern  and  western  parts  of  a  loadstone.  Robert  Norman,  an 
Englishman,  posits  a  point  and  place  toward  which  the 
magnet  looks  (but  whereto  it  is)  not  drawn  :  toward  which 
magnetized  iron,  according  to  him,  is  collimated,  but  which 
does  not  attract  it.  Franciscus  Maurolycus  *  discusses  a  few 
problems  regarding  the  loadstone,  adopting  the  current 
opinions  of  others ;  he  believes  that  the  variation  is  caused  by 

'  An  account  of  Francis  Maurolycus  appears  in  a  note,  Book  I,  Chap.  XVII, 
of  present  work. 


ANCIENT  AND  MODERN  AUTHORS  ON  THE  LOADSTONE,    II 

a  certain  magnetic  island  mentioned  by  Olaus  Magnus. 
Josephus  Costa,  knowing  nothing  whatever  of  the  subject, 
nevertheless  pours  out  empty  words  about  the  loadstone. 
Livio  Sanuto  in  his  Geography  (written  in  Itahan)  discourses 
at  length  of  the  prime  magnetic  meridian,  of  the  magnetic 
poles,  whether  they  are  terrestrial  or  celestial ;  treats  also  of 
an  instrument  for  finding  the  longitude  ;  but  as  he  does  not 
understand  the  nature  of  the  loadstone,  he  does  but  add 
errors  and  obscurities  to  his  otherwise  excellent  treatise. 
Fortunius  Affaitatus  has  some  rather  silly  philosophizing 
about  attraction  of  iron  and  the  turning  toward  the  poles. 
Very  recently  Baptista  Porta,  a  philosopher  of  no  ordinary 
note,  makes  the  7th  book  of  his  Magia  Naturalis  a  very 
storehouse  and  repertory  of  magnetic  wonders ;  but  he  knows 
little  about  the  movements  of  the  loadstone,  and  never  has 
seen  much  of  them  ;  much  of  what  he  has  learned  about  its 
obvious  properties,  either  from  Messer  Paolo,  the  Venetian,  or 
through  his  own  studies,  is  not  very  accurately  noted  and  ob- 
served ;  the  book  is  full  of  most  erroneous  experiments,  as  will 
appear  in  fitting  place ;  still  I  hold  him  worthy  of  praise  for 
that  he  essayed  so  great  a  task  (even  as  he  has  essayed  many 
another  task,  and  successfully  too,  and  with  no  inconsiderable 
results),  and  that  he  has  given  occasion  for  further  researches. 
All  these  philosophers,  our  predecessors,  discoursing  of 
attraction  on  the  basis  of  a  few  vague  and  indecisive  experi- 
ments and  of  reasonings  from  the  recondite  causes  of  things ; 
and  reckoning  among  the  causes  of  the  direction  of  the  magnet, 
a  region  of  the  sky,  celestial  poles,  stars,  asterisms ;  or  moun- 
tains, cliffs,  vacant  space,  atoms,  attractional  or  collimational 
regions  beyond  the  heavens,  and  other  like  unproved  para- 
doxes, are  world-wide  astray  from  the  truth  and  are  blindly 
wandering.     But  we  do  not  propose  just  now  to  overturn  with 


12  WILLIAM  GILBERT. 

arguments  either  these  their  errors  and  impotent  reasonings, 
or  the  other  many  fables  about  the  loadstone,  or  the  fairy-tales 
of  mountebanks  and  story-tellers;  as,  for  example,  the  ques- 
tions raised  by  Franciscus  Rueus  about  the  loadstone,  whether 
it  is  an  imposture  of  cacodaemons ;  or  the  assertion  that  a 
loadstone  placed  unawares  under  the  head  of  a  sleeping  woman 
drives  her  out  of  the  bed  if  she  be  an  adulteress  ;  or  that  by  its 
fume  and  vapor  the  loadstone  is  of  use  to  thieves,  as  though 
the  stone  were  by  nature  given  to  promote  thefts ;  or  that  it 
withdraws  bolts  and  opens  locks,  as  Serapio  insanely  imagines ; 
or  that  iron  held  by  a  loadstone's  attraction,  being  placed  in 
a  balance,  adds  nought  to  the  weight  of  the  loadstone,  as 
though  the  weight  of  the  iron  were  absorbed  by  the  virtue  of 
the  loadstone  ;  or  that,  as  Serapio  and  the  Moors  report,  there 
are  in  Indian  seas  certain  sharp-pointed  rocks  abounding  in 
loadstone,  the  which  draw  every  nail  out  of  ships  that  land 
alongside  them  and  hold  the  vessels :  this  story,  Olaus  Magnus 
does  not  fail  to  recite :  he  tells  of  mountains  in  the  North 
possessing  such  power  of  attraction,  that  ships  have  to  be  con- 
structed with  wooden  pegs,  so  that  as  they  sail  by  the 
magnetic  cliffs  there  be  no  iron  nails  to  draw  out.'     Nor  will 


'  Olaus  Magnus,  Historia  de  Gentibus  Septentrionalibus,  Romae  1555,  Book 
II,  Chap.  XXVI,  page  8g.  This  is  likewise  alluded  to  by  Porta  in  his  Magia 
Naturalis,  1658  ed.,  Book  VII,  Chap.  I,  page  191,  and  1664  ed..  Book  VII, 
Chap.  I,  page  288. 

"Of  Rocks  Magnetical  there  are  likewise  two  relations;  for  some  are 
delivered  to  be  in  the  Indies  and  some  in  the  extremity  of  the  North  and  about 
the  very  Pole.  The  Northern  account  is  commonly  ascribed  unto  Olaus 
Magnus,  Arch-Bishop  of  Upsale,  who  out  of  his  Predecessor,  Joannes,  Saxo, 
and  others  compiled  a  history  of  some  Northern  Nations;  but  this  assertion  we 
have  not  discovered  in  that  work  of  his  which  commonly  passeth  among  us; 
and  should  believe  his  Geography  herein  no  more  then  that  in  the  first  line  of 
his  book;  when  he  affirmeth  that  Biarmia  (which  is  not  70  degrees  in  latitude) 
hath  the  Pole  for  its  Zenith,  and  Equinoctial  for  the  Horizon"  (Thomas  Brown, 
Pseudoloxia  Epidemica,  1658,  Book  II,  page  78).     Consult,  also,  Claudius  Ptolo- 


ANCIENT  AND  MODERN  AUTHORS  ON  THE  lOADSTONE-    1 3 

we  take  the  trouble  to  refute  such  stories  as  that  a  white  load- 
stone may  be  used  as  a  philter  ;  or  that,  as  Abohali  (Hali 
Abbas)  rashly  asserts,  when  held  in  the  hand  it  cures  pains  of 
the  feet  and  cramps ;  or  that,  as  Pictorius  sings,  it  gives  one 
favor  and  acceptance  with  princes  or  makes  one  eloquent ; 
that,  as  Albertus  Magnus  says,  there  are  two  species  of  load- 
stones, one  pointing  north,  the  other  south  ;  or  that  iron  is 
directed  toward  the  northern  stars  by  a  force  communicated 
from  the  polar  stars,  even  as  plants,  like  the  sunflower, 
follow  the  sun ;  or,  as  the  astrologer  Lucas  Gauricus  held,  that 
beneath  the  tail  of  Ursa  Major  is  a  loadstone ;  Lucas  further 
assigns  the  loadstone  (as  the  sardonyx  and  the  onyx)  to  the 
planet  Saturn,  but  also  to  Mars  (with  the  diamond,  jasper,  and 
ruby),  so  that  the  loadstone,  according  to  him,  is  ruled  by  two 
planets  ;  further,  Lucas  says  that  the  loadstone  belongs  to  the 
sign  Virgo  ;  and  with  a  veil  of  mathematical  erudition  does  he 
cover  many  similar  disgraceful  stupidities.  Gaudentius  Merula 
advises  that  on  a  loadstone  be  graven  the  image  of  a  bear, 
when  the  moon  looks  to  the  north,  so  that  being  suspended  by 
an  iron  thread  it  may  win  the  virtue  of  the  celestial  Bear  ; 
Ficinus  writes,  and  Merula  copies,  that  the  loadstone  draws 
iron  and  makes  it  point  north,  because  it  is  of  higher  order 
than  iron  in  the  Bear.  Others  tell  that  in  daytime  the  load- 
stone possesses  the  power  of  attracting  iron,  but  that  at  night 
this  power  is  feeble  or  rather  null ;  Ruellius  writes  that  the 
loadstone's  force,  when  failing  or  dulled,  is  restored  by  the 
blood  of  a  buck  ;  it  has  been  said  that  a  buck's  blood  frees  the 
magnet  from  the  diamond's  sorcery,  giving  back  its  lost  power 


mseus,  Geographia,  Lib.  vii,  c.  2;  Klaproth  Boussole,  Paris  1834,  p.  116,  etc.; 
Taisnier's  Z>^  iVfls/^ra,  1562,  Eden  tr.  p.  12;  "  Beati  Alb.  Magni,  Ratisbonien- 
sis  .  .  .  ,"  Lib.  viii,  Lugduni  1651  ;  J.  H.  Martin,  "  Observ,  et  Theories," 
Rome  1865,  p,  304. 


14  WILLIAM  GILBERT. 

when  the  magnet  is  bathed  in  the  blood — this,  because  of  the 
variance  between  that  blood  and  the  diamond  ;  *  Arnoldus  de 
Villanova  fancies  that  the  loadstone  frees  women  from  witch- 
craft and  puts  demons  to  flight ;  Marbodaeus,  a  Frenchman, 
fugleman  of  vain  imaginings,  says  that  it  can  make  husbands 
agreeable  to  wives  and  may  restore  wives  to  their  husbands ; 
Caelius  Calcagninius  in  his  Relationes  says  that  a  magnet 
pickled  with  salt  of  the  sucking-fish  has  the  power  of  picking 
up  a  piece  of  gold  from  the  bottom  of  the  deepest  well.  In 
such-like  follies  and  fables  do  philosophers  of  the  vulgar  sort 
take  delight;  with  such-like  do  they  cram  readers  a-hungered 
for  things  abstruse,  and  every  ignorant  gaper  for  nonsense. 
But  when  the  nature  of  the  loadstone  shall  have  been  in  the 
discourse  following  disclosed,  and  shall  have  been  by  our 
labors  and  experiments  tested,  then  will  the  hidden  and  recon- 
dite but  real  causes  of  this  great  effect  be  brought  forward, 
proven,  shown,  demonstrated ;  then,  too,  v/ill  all  darkness 
vanish ;  every  smallest  root  of  error,  being  plucked  up,  will  be 
cast  away  and  will  be  neglected;  and  the  foundations  of  a 
grand  magnetic  science  being  laid  will  appear  anew,  so  that 
high  intellects  may  no  more  be  deluded  by  vain  opinions. 

There  are  other  learned  men  who  on  long  sea  voyages 
have  observed  the  differences  of  magnetic  variation ;  as  that 
most  accomplished  scholar  Thomas  Hariot,  Robert  Hues, 
Edward  Wright,  Abraham  Kendall,  all  Englishmen ;  others 
have  invented  and  published  magnetic  instruments  and  ready 
methods  of  observing,  necessary  for  mariners  and  those  who 
make  long  voyages :  as  William  Borough  in  his  little  work  the 
Variation   of  the    Compass,    Williani    Barlo   (Barlowe)   in    his 

1  Consult:  Simon,  Clavis  Sanationis,  Padua  1474;  C.  G.  Solino,  Folykisior, 
p.  154,  Lyons  ed.  1538;  Vincentii  Burgundi,  Spec.  Mai.  T.  i.  Lib.  8,  c.  40, 
Douai  ed.  1624. 


THE  LOADSTONE:     WHAT  IT  IS:    ITS  DISCOVERY.       1 5 

Supplement,  Robert  Norman  in  his  New  Attractive — the  same 
Robert  Norman,  skilled  navigator  and  ingenious  artificer,  who 
first  discovered  the  dip  of  the  magnetic  needle/  Many  others 
I  pass  by  of  purpose :  Frenchmen,  Germans,  and  Spaniards  of 
recent  time  who  in  their  writings,  mostly  composed  in  their 
vernacular  languages,  either  misuse  the  teachings  of  others, 
and  like  furbishers  send  forth  ancient  things  dressed  with  new 
names  and  tricked  in  an  apparel  of  new  words  as  in  prosti- 
tutes' finery ;  or  who  publish  things  not  even  worthy  of  record; 
who,  pilfering  some  book,  grasp  for  themselves  from  other 
authors,  and  go  a-begging  for  some  patron,  or  go  a-fishing 
among  the  inexperienced  and  the  young  for  a  reputation  ;  who 
seem  to  transmit  from  hand  to  hand,  as  it  were,  erroneous 
teachings  in  every  science  and  out  of  their  own  store  now  and 
again  to  add  somewhat  of  error. 


CHAPTER  II. 

THE  LOADSTONE:  WHAT  IT  IS:  ITS  DISCOVERY. 

This  stone  is  commonly  called  magnet,  either  after  its 
finder  {not  Pliny's  mythical  herdsman — copied  from  Nicander 
—  the  hobnails  of  whose  brogues  and  the  point  of  whose  staff 

'  Whewell  thus  renders  the  passage  ("  Hist.  Ind.  Sc",  1859,  Vol.  II,  page 
218):  "  Other  learned  men  have,  in  long  navigations,  observed  the  differences 
of  magnetic  variations,  as  Thomas  Hariot,  Robert  Hues,  Edward  Wright, 
Abraham  Kendall,  all  Englishmen:  others  have  invented  magnetic  instruments 
and  convenient  modes  of  observation,  such  as  are  requisite  for  those  who  take 
long  voyages,  as  William  Borough  in  his  Book  concerning  the  variation  of  the 
compass,  William  Barlo  in  his  Supplement,  Robert  Norman  in  his  'New  At- 
tractive.' This  is  that  Robert  Norman  (a  good  seaman  and  an  ingenious 
artificer)  who  first  discovered  the  dip  of  magnetic  iron."  This  important  dis- 
covery was  made  in  1576  ("  Enc.  Met.",  page  738).  Read  paragraph  366  of  J. 
F.  W.  Herschel's  "Prelim.  Disc",  1855. 


1 6  ■      WILLIAM  GILBERT. 

were  held  fast  in  a  magnetic  region  while  he  was  pasturing  his 
cattle),  or  after  the  district  Magnesia  in  Macedonia/  abound- 
ing in  loadstones ;  or  after  the  City  of  Magnesia  in  Ionia  of 
Asia  Minor,  on  the  river  Maender ;  hence  Lucretius  writes, 
Quern  Magneta  vacant  patrio  de  nomine  Graii,  Magnetum  quia 
sit  patriis  in  montibus  ortus^  It  is  called  Heracleus  from  the 
City  Heraclea,^  or  after  that  unconquerable  hero  Hercules, 
because  of  its  great  strength  and  its  power  and  dominion  over 
iron  which  is  thesubduer  of  all  things;  it  is  also  called  Sideritis, 
as  though  one  should  say  Ferrarius  {Ferrarius  lapis — iron- 
stone). It  was  not  unknown  to  the  earliest  writers,  whether 
among  the  Greeks,  as  Hippocrates  and  others,  or  (as  I  believe) 
among  the  Jews  and  the  Egyptians ;  for  in  the  most  ancient 
iron  mines,  in  particular  the  most  famous  mines  of  Asia,  the 
loadstone,  brother  uterine  of  iron,  was  oft  dug  out  in  company 
with  that  ore.     And  if  those  things  be  true  which   are  told 

'  Magnesia.  Many  authors  erroneously  allude  to  a  city  or  town  called 
Magnesia — in  the  country  of  Magnesia — in  Thessaly,  one  of  the  number  being 
the  learned  Dr.  W.  Smith,  who  further  states  ("  Diet,  of  Greek  and  Roman 
Geogr.",  1857,  Vol.  II,  page  1170)  that  the  Thessalian  Magnetes — Magnesians — 
are  said  to  have  founded  both  the  Ionian  and  the  Lydian  Magnesias.  The 
celebrated  historian  Barthold  George  Niebuhr,  in  his  "  Lectures  on  Ancient 
Ethnography  and  Geography,"  states  (transl.  of  Dr.  L.  Schmitz,  London  1853, 
Vol.  I,  page  168)  that  the  "town  of  Magnesia  never  existed,  it  is  a  mere  blun- 
der, .  .  .  not  mentioned  by  either  Scylax,  Herodotus,  or  Demosthenes,"  and, 
furthermore,  that  the  province  of  Magnesia  was  governed  by  the  Macedonians, 
and  that  it  is  not  probable  it  was  ever  incorporated  by  the  Romans  with 
either  Thessaly  or  Macedonia. 

'^  Transl. — Which  the  Greeks  call  magnetes,  from  the  name  of  its  country, 
for  it  had  its  origin  in  the  native  hills  of  the  Magnesians. 

'  Heraclea,  a  town  of  uncertain  site  in  Lydia,  perhaps  not  far  from  (the 
Lydian)  Magnesia  at  the  foot  of  Mount  Sipylus  {ad  Sipylum)  (Dr.  W.  Smith, 
"Diet,  of  Greek  and  Roman  Geogr.",  1857,  Vol.  I,  page  1049).  Gilbert  has 
alluded  to  the  celebrated  Magnesia  in  Ionia  {ad  Maendrum),  but  it  is  uncertain 
which  of  the  two  Magnesias  is  really  meant  (Ninth  "  Encycl.  Brit.",  Vol.  XV, 
page  219,  note).  At  page  470,  Vol.  VI,  of  the  "  Diet.  Geogr.  Univ.",  Paris  1829, 
it  is  said  that  it  was  the  Magnesia  ad  Sipylum — Manika-Mansa — which  gave  its 
name  to  the  Magnes,  and  this  view  is  taken  by  many  authors. 


THE  LOADSTONE:     WHAT  IT  IS:    ITS  DISCOVERY.        1 7 

about  the  people  of  China,  neither  were  they  in  primitive 
times  ignorant  of  magnetic  experiments,  for  even  in  their 
country  are  seen  the  most  excellent  magnets  in  the  world. 
The  Egyptians,  as  Manetho  relates,  give  it  the  name  of  '  the 
bone  of  Horus,'  calling  the  potency  that  presides  over  the 
revolution  of  the  sun  Horus,  as  the  Greeks  called  it  Apollo. 
But  later,  as  Plato  declares,  Euripides  gave  to  it  the  name 
magnet.  It  is  mentioned  and  praised  by  Plato  in  the  lo,  by 
Nicander  of  Colophon,  Theophrastus,  Dioscorides,  Pliny,  Soli- 
nus,  Ptolemy,  Galen,  and  other  investigators  of  nature.  But 
considering  tbe  great  differences  of  loadstones,  their  dissim- 
ilitude in  hardness,  softness,  heaviness,  lightness,  density, 
firmness,  friableness :  in  color  and  in  all  other  qualities  ;  these 
writers  have  not  handed  down  any  sufiEicient  account  of  it. 
The  history  of  the  magnet  was  overlooked  by  them,  or,  if 
written,  was  incompletely  given,  because  in  olden  time  objects 
of  many  kinds  and  foreign  products  never  before  seen  were 
not  brought  in  by  traders  and  mariners  as  they  are  wont  to 
be  brought  in  now,  when  all  manner  of  commodities — stones, 
woods,  spices,  herbs,  metals,  and  metallic  wares — are  eagerly 
sought  for  all  over  the  earth ;  neither  was  mining  carried  on 
everywhere  in  early  times  as  it  is  now. 

The  difference  between  loadstones  rests  on  their  respective 
power  :  hence  one  loadstone  is  male,  another  female :  so  the 
ancients  were  wont  to  distinguish  many  objects  of  the  same 
species.  Phny  quotes  from  Sotacus  five  kinds,  viz.  :  the  load- 
stones of  Ethiopia,  Macedonia,  Boeotia,  Troas,  and  Asia,  re- 
spectively, which  were  the  chief  sorts  known  to  the   ancients.' 


>  Porta  has  it:  "The  Ethiopian,  the  Magnesian  from  Magnesia  near 
Macedonia,  as  the  way  lies  to  the  Lake  Boebis,  on  the  right  hand;  the  third  in 
Echium  of  Boetia,  the  fourth  about  Alexandria  at  Troaderum;  the  fifth  in 
Magnesia  of  Asia"  ("Nat.  Mag.,"  Book  VII,  Chap.  I). 


lo  WILLIAM  GILBERT. 

But  we  recognize  as  many  kinds  as  there  are  in  the  whole  world 
regions  differing  in  soil ;  for  in  every  clime,  in  every  province, 
in  all  kinds  of  land,  either  the  loadstone  is  found  or  lies  un- 
known because  of  its  deep  site  or  its  inaccessible  situation  ;  or, 
because  of  its  weaker  and  less  potent  virtues,  it  is  not  recog- 
nized by  us  the  while  we  see  it  and  touch  it.' 

For  the  ancients,  the  differences  were  based  on  the  color  : 
The  magnets  from  Magnesia  in  Macedonia  were  red  and  black, 
those  from  Boeotia  red  rather  than  black,  those  from  the  Troad 
black  without  strength,  those  from  Asian  Magnesia  white, 
without  power  of  attracting  iron,  and  resembling  pumice.  A 
strong  loadstone  and  one  that  under  experiment  demonstrates 
its  power,  nowadays  generally  resembles  unpolished  iron  and 
usually  is  found  in  iron  mines  :  sometimes  it  is  found  also  form- 
ing a  continuous  vein  by  itself;  such  loadstones  are  imported 
from  the  East  Indies,  China,  and  Bengal,  and  they  are  of  the 
color  of  iron,  or  of  a  dark  blood-red  or  liver  color.  These  are 
the  most  excellent  and  often  are  of  great  size  and  weight,  as  if 
broken  off  a  great  rock ;  or  again  they  are  as  if  complete  in 
themselves.  Some  of  these,  though  they  may  weigh  but  one 
pound,  will  lift  4  ounces,  or  half  a  pound,  or  even  an  entire 
pound  of  iron.  In  Arabia  are  found  red  loadstones  shaped 
like  tiles,  not  as  heavy  as  those  imported  from  China,  yet  strong 
and  good.  Rather  black  loadstones  are  found  in  Ilva,  an  island 
of  the  Etrurian  sea ;  with  these  occur  also  white  loadstones 
like  those  from  the  mines  of  Caravaca  in  Spain  :  but  they  are 
of  inferior  strength.  Black  loadstones  also  are  found,  and 
these,  too,  are  rather  inferior  in  strength,  for  example,  those 
met  with  in  the  iron  mines  of  Norway  and  in  the  coast  region 


'  Consult  Johann    S.  T.  Gehler's    "  Physikalisches    Worterbuch,"    article 
"  Magnetismus." 


THE  LOADSTONE:     WHAT  IT  IS:    ITS  DISCOVERY.       1 9 

along  the  Cattegat.  Blue-black  and  dusky-blue  loadstones  are 
likewise  powerful  and  highly  prized.'  But  there  are  others  of  a 
lead  color,  fissile  or  not  fissile,  that  can  be  split  up  like  slate  ; 
I  have  also  loadstones  resembling  an  ashy-gray  marble,  mottled 
like  gray  marble  :  these  take  a  high  polish.  In  Germany,  are 
loadstones  perforated  like  the  honeycomb  :  these  are  lighter 
than  the  other  sorts,  yet  they  are  powerful.  The  metallic  load- 
stones are  those  which  are  smelted  into  the  best  of  iron  ;  the 
rest  are  not  easily  smelted,  but  are  burnt. 

There  are  loadstones  that  are  very  heavy,  as  there  are  others 
very  light ;  some  are  very  powerful  and  carry  masses  of  iron  ; 
others  are  weaker  and  less  powerful ;  some  so  faint  and  void  of 
strength  that  they  can  hardly  attract  ever  so  small  a  piece  of 
iron,  nor  do  they  repel  an  opposite  magnetized  body.  Others 
are  firm  and  tough,  nor  are  they  easy  to  work  ;  others  are  fri- 
able. Again,  some  are  dense  and  hard  Hke  corundum,  or  light 
or  soft  like  pumice;  porous  or  solid  ;  smooth  and  uniform,  or 
irregular  and  corroded.  Now  hard  as  iron,  nay  sometimes 
harder  to  cut  or  to  file  than  iron  ;  again  as  soft  as  clay.  Not 
all  magnets  can  properly  be  called  stones  :  some  there  are  that 
represent  rather  rocks  ;  others  are  rather  metallic  ores  ;  others 
are  like  clods  of  earth.  So  do  they  vary  and  differ  from  one 
another,  and  some  possess  more,  others  less,  of  the  peculiar 
magnetic  virtue.  For  they  differ  according  to  the  nature  of 
the  soil,  and  the  different  mixtures  of  clays  and  humors  ;  ac- 
cording to  the  lie  of  the  land  and  the  decay  of  this  highest 
substance  born  to  Earth  :  decay  due  to  the  concurrence  of  many 


'  "They  are  proved  to  be  the  best  which  are  most  of  blewe  or  heavenly- 
colour  "  (Taisnier,  Z>^  A^a^wrrt,  1562,  Eden  tr.  p.  ii). — "It  is  certain,  that  the 
bluer  they  are,  the  better  they  are  "  (Porta,  "Natural  Magick,"  1658,  Chap. 
VII,  page  191).  Consult  Epistola  P.  Peregrini  De  Magnete,  Cap.  Ill,  and 
Barthol.  de  Glanvil,  Lib.  de  Prop.,  Lyons  1480,  fol..  Lib.  XVI,  Cao.  LXII. 


20  WILLIAM   GILBERT. 

causes  and  the  never-ceasing  vicissitude  of  rise  and  decline  and 
the  mutations  of  bodies.  Nor  is  this  stone,  endowed  as  it  is 
with  such  power,  a  rarity  :  there  is  no  country  wherein  it  may 
not  be  found  in  one  form  or  other.  But  were  men  to  seek  it 
more  dihgently  and  at  greater  expense,  and  could  they  in  the 
face  of  difficulties  mine  it,  it  might  be  obtained  everywhere, 
as  later  we  will  prove.  In  many  regions  are  found  and  are  now 
opened  mines  of  powerful  loadstones  unknown  to  ancient 
authors,  in  Germany,  for  example,  where  none  of  them  ever 
said  that  loadstones  were  mined  ;  and  yet  since  the  time  within 
the  memory  of  our  fathers  when  the  business  of  mining  began 
there  to  be  developed,  in  many  parts  of  Germany  powerful 
loadstones  of  great  virtues  have  been  taken  out  of  the  earth,  as 
in  the  Black  Forest  near  Helceburg :  in  Mt.  Misena  not  far 
from  Schwarzberg  ;  some  of  considerable  strength  from  the 
region  betwixt  Schneeberg  and  Annaberg  in  the  Joachimsthal, 
as  was  observed  by  Cordus  ;  also  near  Pela  in  Franconia  ;  in 
Bohemia  from  the  iron  mines  near  Lesse  ;  and  in  other  places, 
as  we  are  informed  by  Georgius  Agricola  and  other  men  learned 
in  the  art  of  mining.  The  like  is  to  be  said  of  other  countries 
in  our  time  ;  for  this  stone,  famous  for  its  virtues,  as  to-day  it 
is  well  known  throughout  the  world,  so  is  produced  in  every 
land  ;  it  is,  so  to  speak,  a  native  of  all  countries.  In  East  India, 
in  China,  in  Bengal,  along  the  banks  of  the  Indus,  it  is  plenti- 
ful, also  in  certain  marine  rocks  ;  in  Persia,  too,  in  Arabia  and 
the  isles  of  the  Red  Sea  ;  in  many  parts  of  Ethiopia,  as  was 
anciently  Zimiri,  mentioned  by  Pliny  ;  in  Asia  Minor  around 
Alexandria,  Boeotia,  Italy,  the  island  Elba,  Barbary  ;  in  Spain, 
still  in  many  localities  as  of  old  ;  in  England  quite  recently  a 
vast  quantity  was  found  in  a  mine  owned  by  a  gentleman,  named 
Adrian  Gilbert,  as  also  in  Devonshire  and  in  the  Forest  of 
Dean  ;  in  Ireland  too,  in  Norway,  Denmark,  Sweden,  Lapland. 


THE  LOADSTONE:     WHAT  IT  IS:    ITS  DISCOVERY.       21 

Livonia,  Prussia,  Poland,  Hungary/  For  albeit  the  terrestrial 
globe,  various  humors  and  diversities  of  soils  being  produced 
by  the  perpetual  vicissitude  of  generation  and  decay,  is  ever  to 
a  greater  and  greater  depth  beneath  the  surface  in  the  lapse  of 
ages  efflorescing,  and  is  being  clothed  as  it  were  with  a  diversi- 
fied and  perishable  covering  and  wrappage  ;  still  from  its  in- 
terior arises  in  many  places  a  progeny  nigher  to  the  more  per- 
fect bbdy,  and  makes  its  way  into  the  sunlit  air.  But  the  weak 
loadstones  and  those  of  less  strength,  which  thus  have  been 
deprived  of  their  virtue  by  being  soaked  v»^ith  humors,  are 
visible  everywhere,  in  every  country-side  ;  great  masses  of  these 
are  to  be  found  in  every  quarter,  without  tunnelling  mountains 
or  sinking  mines,  and  without  any  of  the  toils  and  difficulties 
of  mining,  as  we  will  show  in  the  sequel.  These  we  will  so 
manipulate  according  to  a  simple  process,  that  their  languid 
and  dormant  properties  shall  be  made  manifest. 

The  magnet  is  called  by  the  Greeks  'HpocKXeioZ,  as  by  Theo- 
phrastus,  and  Mayvf/ris  and  Mayvijs,  as  by  Euripides,  quoted 
by  Plato  in  the  lo;  by  Orpheus  it  is  called  also  MayvT^ocra  and 
2idrjpitr)Z  {quasi  ironstone)  ;  by  the  Latins  it  is  called  Magnes 
Herculeus  ;  by  the  French  Aimant,  a  corruption  of  adamas ; 
hy  the  SpsLniards  Ptedramanf ;  by  the  Italians  Calamita ;  by 
the  English  XoabStOne  an&  HC)amant  stone;  by  the  Germans 
Magness  and  Siegelstein.  Among  the  English,  French,  and 
Spaniards,  it  has  its  common  name  from  adamas,  and  this  is 
probably  because  at  some  time  those  people  were  led  astray 
by  the  term  siderites,  which  was  applied  both  to  the  diamond 
and  the  magnet.^     The  magnet  is  called  ^idrjpitij's   because 

'  "The  most  powerful  native  magnets  are  found  in  Siberia,  and  in  the 
Hartz;  they  are  also  obtainable  on  the  Island  of  Elba  "  (Dana).  See  Gilbert, 
Book  IV,  Chap.  V. 

*  Consult  Vincentii  Burgundi,  Spec.  Mai.,  Douai  ed.  1624,  T.  I,  LVIII, 
C.  34,  39-41;  Alb.  Magnus,  De  Mineral.,  Op.  T.  II,  Lione  1651,  Tr.  II,  C.  I. 


22  WILLIAM  GILBERT. 

of  its  property  of  attracting  iron ;  and  the  diamond  is  called 
2i6rfpiTT/5  from  the  glistening  of  polished  iron-  Aristotle 
merely  names  the  loadstone  in  his  work  De  Anima,  I. :  "Eoiks 
6e  Kai  ©aXfjS  e^  d)v  oc7iojj.vejxovevov(Tif  Kivr/riKOv  n  rrfv 
ipvx^y  iTtoXafx^aveiv,  eirtep  rov  Xidov  ipvx'ijy  e(prf  exeiv^  on 
tor  cridr/pov  Kivet.  (Thales,  too,  seems,  from  what  they  relate, 
to  regard  the  soul  as  somewhat  producing  motion,  for  he  said 
that  this  stone  has  a  soul,  since  it  moves  iron.)  The  name 
magnet  is  also  given  to  another  stone  differing  widely  from 
the  siderites,  and  having  the  look  of  silver:  in  its  nature 
this  stone  resembles  amianth  (asbestus),  and  in  form  differs 
from  that  inasmuch  as  it  consists,  like  mica,  of  laminae ;  the 
Germans  call  it  Katsensilber  and  Talk. 


CHAPTER    III. 

THE  LOADSTONE  POSSESSES  PARTS  DIFFERING  IN  THEIR  NAT- 
URAL POWERS,  AND  HAS  POLES  CONSPICUOUS  FOR  THEIR 
PROPERTIES. 

The  many  qualities  exhibited  by  the  loadstone  itself, 
qualities  hitherto  recognized  yet  not  well  investigated,  are  to 
be  pointed  out  in  the  first  place,  to  the  end  the  student  may 
understand  the  powers  of  the  loadstone  and  of  iron,  and  not 
be  confused  through  want  of  knowledge  at  the  threshold  of 
the  arguments  and  demonstrations.  In  the  heavens,  astrono- 
mers give  to  each  moving  sphere  two  poles ;  thus  do  we  find 

page  227,  and  C.  XI,  page  233;  C.  G.  Solino,  Exercitationes  Plin.,  Rhenuni 
1689,  page  log.  The  Macedonian  diamond,  as  well  as  the  adamas  cyprius  and 
siderites,  were  obviously  not  dianaonds,  but  soft  stones  (Thomson,  "  Hist,  of 
Chem.",  1830,  Vol.  I,  page  98). 


QUALITIES  OF    THE  LOADSTONE.  2$ 

two  natural  poles  of  excelling  importance  even  in  our  terres- 
trial globe,  constant  points  related  to  the  movement  of  its 
daily  revolution,  to  wit,  one  pole  pointing  to  Arctos  (Ursa)  and 
the  north ;  the  other  looking  toward  the  opposite  part  of  the 
heavens.  In  like  manner  the  loadstone  has  from  nature  its 
two  poles,  a  northern  and  a  southern  ;  fixed,  definite  points  in 
the  stone,  which  are  the  primary  termini  of  the  movements 
and  effects,  and  the  limits  and  regulators  of  the  several  actions 
and  properties.  It  is  to  be  understood,  however,  that  not  from 
a  mathematical  point  does  the  force  of  the  stone  emanate,  but 
from  the  parts  themselves ;  and  all  these  parts  in  the  whole — 
while  they  belong  to  the  whole — the  nearer  they  are  to  the 
poles  of  the  stone  the  stronger  virtues  do  they  acquire  and 
pour  out  on  other  bodies.  These  poles  look  toward  the  poles 
of  the  earth,  and  move  toward  them,  and  are  subject  to  them. 
The  magnetic  poles  may  be  found  in  every  loadstone,  whether 
strong  and  powerful  (male,  as  the  term  was  in  antiquity)  or 
faint,  weak,  and  female ;  whether  its  shape  is  due  to  design  or 
to  chance,  and  whether  it  be  long,  or  flat,  or  four-square,  or 
three-cornered,  or  polished ;  whether  it  be  rough,  broken-off, 
or  unpolished  :  the  loadstone  ever  has  and  ever  shows  its  poles.  * 
But  inasmuch  as  the  spherical  form,  which,  too,  is  the  most 
perfect,  agrees  best  with  the  earth,  which  is  a  globe,  and  also 
is  the  form  best  suited  for  experimental  uses,  therefore  we  pur- 
pose to  give  our  principal  demonstrations  with  the  aid  of  a 
globe-shaped  loadstone,  as  being  the  best  and  the  most  fitting. 
Take  then  a  strong  loadstone,  solid,  of  convenient  size,  uni- 
form, hard,  without  flaw ;  on  a  lathe,  such  as  is  used  in  turning 
crystals  and  some  precious  stones,  or  on  any  like  instrument 
(as  the  nature  and  toughness  of  the  stone  may  require,  for  often 
it  is  worked  only  with  difficulty),  give  the  loadstone  the  form 
of  a  ball.     The  stone  thus  prepared  is  a  true  homogeneous  ojff- 


24  WILLIAM  GILBERT. 

spring  of  the  earth  and  is  of  the  same  shape,  having  got  from 
art  the  orbicular  form  that  nature  in  the  beginning  gave  to  the 
earth,  the  common  mother ;  and  it  is  a  natural  little  body  en- 
dowed with  a  multitude  of  properties  whereby  many  abstruse 
and  unheeded  truths  of  philosophy,  hid  in  deplorable  dark- 
ness, may  be  more  readily  brought  to  the  knowledge  of  man- 
kind. To  this  round  stone  we  give  the  name  MiKpoyr}  (microge) 
or  Terrella  (earthkin,  little  earth).' 

To  find,  then,  poles  answering  to  the  earth's  poles,  take  in 
your  hand  the  round  stone,  and  lay  on  it  a  needle  or  a  piece  of 
iron  wire  :  the  ends  of  the  wire  move  round  their  middle  point, 
and  suddenly  come  to  a  standstill.  Now,  with  ochre  or  with 
chalk,  mark  where  the  wire  lies  still  and  sticks.  Then  move 
the  middle  or  centre  of  the  wire  to  another  spot,  and  so  to  a 
third  and  a  fourth,  always  marking  the  stone  along  the  length 
of  the  wire  where  it  stands  still :  the  lines  so  marked  will  ex- 
hibit meridian  circles,  or  circles  like  meridians  on  the  stone  or 
terrella  ;  and  manifestly  they  will  all  come  together  at  the  poles 
of  the  stone.  The  circles  being  continued  in  this  way,  the 
poles  appear,  both  the  north  and  the  south,  and  betwixt  these, 
midway,  we  may  draw  a  large  circle  for  an  equator,  as  is  done  by 
the  astronomer  in  the  heavens  and  on  his  spheres  and  by  the 
geographer  on  the  terrestrial  globe ;  for  the  line  so  drawn  on 
this  our  terrella  is  also  of  much  utility  in  our  demonstrations 
and  our  magnetic  experiments.  Poles  are  also  found  in  the 
round  stone,  in  a  versorium,  in  a  piece  of  iron  touched  with  a 
loadstone  and  resting  on  a  needle  or  point  (attached  at  its 
base  to  the  terrella),  so  that  it  can  freely  revolve,  as  in  the 
figure. 

1  Sir  Kenelm  Digby,  "A  Treatise  of  Bodies,"  London  1645,   Chap.  XX, 
page  225. 


QUALITIES  OF   THE  LOADSTONE. 


25 


On  top  of  the  stone  AB  is  set  the  versorium  in  such  a 
way  that  its  pointer  may  remain  in  equihbrium  :  mark  with 
chalk  the  direction  of  the  pointer  when  at  rest.  Then  move 
the  instrument  to  another  spot  and  again  mark  the  direction 
in  which  the  pointer  looks ;  repeat  this  many  times  at  many 
different  points  and  you  will,  from  the  convergence  of  the 
lines  of  direction,  find  one  pole  at  the  point  A,  the  other  at 
B,    A  pointer  also  indicates  the  true  pole  if  brought  near  to 


the  stone,  for  it  eagerly  faces  the  stone  at  right  angles,  and 
seeks  the  pole  itself  direct  and  turns  on  its  axis  in  a  right 
line  toward  the  centre  of  the  stone.  Thus  the  pointer  D* 
regards  A  and  F,  the  pole  and  the  centre,  but  the  pointer  E 
looks  not  straight  either  toward  the  pole  A  or  the  centre  F. 
A  bit  of  fine  iron  wire  as  long  as  a  barley-corn  is  laid  on  the 
stone  and  is  moved  over  the  zones  and  the  surface  of  the 
stone  till  it  stands  perpendicularly  erect ;  for  at  the  poles, 
whether  N.  or  S.,  it  stands  erect ;  but  the  farther  it  is  from  the 
poles  (towards  the  equator)  the  more  it  inclines.  The  poles 
thus  found,  you  are  to  mark  with  a  sharp  file  or  a  gimlet. 


^  WILLIAM  GILBERT. 


% 


CHAPTER  IV. 

WHICH    POLE    IS    THE    NORTH  :    HOW    THE    NORTH    POLE    IS 
DISTINGUISHED  FROM  THE  SOUTH  POLE. 

One  of  the  earth's  poles  is  turned  toward  Cynosura  and 
steadily  regards  a  fixed  point  in  the  heavens  (save  that  it  is 
unmoved  by  the  precession  of  the  fixed  stars  in  longitude, 
which  movement  we  recognize  in  the  earth,  as  we  shall  later 
show) ;  the  other  pole  is  turned  toward  the  opposite  aspect  of 
the  heavens,  an  aspect  unknown  to  the  ancients,  but  which  is 
adorned  with  a  multitude  of  stars,  and  is  itself  a  striking  spec- 
tacle for  those  who  make  long  voyages.  So,  too,  the  loadstone 
possesses  the  virtue  and  power  of  directing  itself  toward  the 
north  and  the  south  (the  earth  itself  co-operating  and  giving 
to  it  that  power)  according  to  the  conformation  of  nature, 
which  adjusts  the  movements  of  the  stone  to  its  true  locations. 
In  this  manner  it  is  demonstrated :  Put  the  magnetic  stone 
(after  you  have  found  the  poles)  in  a  round  wooden  vessel — a 
bowl  or  a  dish  ;  then  put  the  vessel  holding  the  magnet  (like  a 
boat  with  a  sailor  in  it)  in  a  tub  of  water  or  a  cistern  where  it 
may  float  freely  in  the  middle  without  touching  the  rim,  and 
where  the  air  is  not  stirred  by  winds  (currents)  which  might 
interfere  with  the  natural  movement  of  the  stone :  there  the 
stone,  as  if  in  a  boat  floating  in  the  middle  of  an  unruflfled 
surface  of  still  water,  will  straightway  set  itself,  and  the  vessel 
containing  it  in  motion,  and  will  turn  in  a  circle  till  its  south 
pole  shall  face  north  and  its  north  pole,  south.  For,  from  a 
contrary  position,  it  returns  to  the  poles  ;  and  though  with  its 


WHICH  POLE  IS   THE  NORTH.  ^7 

first  too  strong  impetus  it  passes  beyond,  still,  as  it  comes 
back  again  and  again,  at  last  it  rests  at  the  poles  or  in  the 
meridian  (save  that,  according  to  the  place,  it  diverges  a  very 
little  from  those  points,  or  from  the  meridional  line,  the  cause 
of  which  we  will  define  later).  As  often  as  you  move  it  out  of 
its  place,  so  often,  by  reason  of  the  extraordinary  power  with 
which  nature  has  endowed  it,  does  it  seek  again  its  fixed  and 
determinate  points.  Nor  does  this  occur  only  when  the  poles 
of  the  loadstone  in  the  float  are  made  to  lie  evenly  in  the 
plane  of  the  horizon  ;  it  takes  place  also  even  though  one  pole, 
whether  north  or  south,  be  raised  or  depressed  lo,  20,  30,  40, 
or  80  degrees  from  the  plane  of  the  horizon ;  you  shall  see  the 
north  part  of  the  stone  seek  the  south,  and  the  south  part  the 
north  ;  so  that  if  the  pole  of  the  stone  be  but  one  degree  from 
the  zenith  and  the  centre  of  the  heavens,  the  whole  stone  re- 
volves until  the  pole  finds  its  own  place  ;  and  though  the  pole 
does  not  point  exactly  to  its  seat,  yet  it  will  incline  toward  it, 
and  will  come  to  rest  in  the  meridian  of  its  true  direction. 
And  it  moves  with  the  same  impetus  whether  the  north  pole 
be  directed  toward  the  upper  heavens,  or  whether  the  south 
pole  be  raised  above  the  horizon.  Yet  it  must  always  be 
borne  in  mind  that  though  there  are  manifold  differences  be- 
tween stones,  and  one  far  surpasses  another  in  virtue  and  effi- 
ciency, still  all  loadstones'have  the  same  limits  and  turn  to  the 
same  points.  Further,  it  is  to  be  remembered  that  all  who 
hitherto  have  written  about  the  poles  of  the  loadstone,  all  in-* 
strument-makers,  and  navigators,  are  egregiously  mistaken  in 
taking  for  the  north  pole  of  the  loadstone  the  part  of  the 
stone  that  inclines  to  the  north,  and  for  the  south  pole  the 
part  that  looks  to  the  south :  this  we  will  hereafter  prove  to 
be  an  error.  So  ill-cultivated  is  the  whole  philosophy  of  the 
magnet  still,  even  as  regards  its  elementary  principles. 


28  WILLIAM  GILBERT. 


CHAPTER   V. 

ONE  LOADSTONE  APPEARS  TO  ATTRACT  ANOTHER  IN  THE 
NATURAL  POSITION  ;  BUT  IN  THE  OPPOSITE  POSITION 
REPELS   IT   AND  BRINGS   IT   TO   RIGHTS. 

First  we  have  to  describe  in  popular  language  the  potent 
and  familiar  properties  of  the  stone ;  afterward,  very  many- 
subtile  properties,  as  yet  recondite  and  unknown,  being  in- 
volved in  obscurities,  are  to  be  unfolded ;  and  the  causes  of  all 
these  (nature's  secrets  being  unlocked)  are  in  their  place  to  be 
demonstrated  in  fitting  words  and  with  the  aid  of  apparatus. 
The  fact  is  trite  and  familiar,  that  the  loadstone  attracts  iron ; 
in  the  same  way,  too,  one  loadstone  attracts  another.  Take 
the  stone  on  which  you  have  designated  the  poles,  N.  and  S., 
and  put  it  in  its  vessel  so  that  it  may  float ;  let  the  poles  he 
just  in  the  plane  of  the  horizon,  or  at  least  in  a  plane  not  very 
obhque  to  it ;  take  in  your  hand  another  stone  the  poles  of 
which  are  also  known,  and  hold  it  so  that  its  south  pole  shall 
he  toward  the  north  pole  of  the  floating  stone,  and  near  it 
alongside  ;  the  floating  loadstone  wiU  straightway  follow  the 
other  (provided  it  be  within  the  range  and  dominion  of  its 
powers),  nor  does  it  cease  to  move  nor  does  it  quit  the  other 
till  it  clings  to  it,  unless,  by  moving  your  hand  away,  you  man- 
age skilfully  to  prevent  the  conjunction.  In  like  manner,  if 
you  oppose  the  north  pole  of  the  stone  in  your  hand  to  the 
south  pole  of  the  floating  one,  they  come  together  and  follow 
each  other.  For  opposite  poles  attract  opposite  poles.  But, 
now,  if  in  the  same  way  you  present  N.  to  N.  or  S.  to  S.,  one 


ONE  LOADSTONE  APPEARS    TO  ATTRACT  ANOTHER. 


29 


stone  repels  the  other ;  and  as  though  a  helmsman  were  bear- 
ing on  the  rudder  it  is  off  like  a  vessel  making  all  sail,  nor 
stands  nor  stays  as  long  as  the  other  stone  pursues.  One 
stone  also  will  range  the  other,  turn  the  other  around,  bring  it 
to  right  about  and  make  it  come  to  agreement  with  itself. 
But  when  the  two  come  together  and  are  conjoined  in  nature's 
order,  they  cohere  firmly.  For  example,  if  you  present  the 
north  pole  of  the  stone  in  your  hand  to  the  Tropic  of  Capri- 


corn (for  so  we  may  distinguish  with  mathematical  circles  the 
round  stone  or  terrella,  just  as  we  do  the  globe  itself)  or  to 
any  point  between  the  equator  and  the  south  pole :  immedi- 
ately the  floating  stone  turns  round  and  so  places  itself  that 
its  south  pole  touches  the  north  pole  of  the  other  and  is  most 
closely  joined  to  it.  In  the  same  way  you  will  get  like  effect 
at  the  other  side  of  the  equator  by  presenting  pole  to  pole ; 
and  thus  by  art  and  contrivance  we  exhibit  attraction  and  re- 
pulsion, and  motion  in  a  circle  toward  the  concordant  position, 
and  the  same  movements  to  avoid  hostile  meetings.  Further- 
more, in  one  same  stone  we  are  thus  able  to  demonstrate  all 


30  WILLIAM  GILBERT. 

this:  but  also  we  are  able  to  show  how  the  self-same  part  of 
one  stone  may  by  division  become  either  north  or  south. 
Take  the  oblong  stone  ad  in  which  a  is  the  north  pole  and 
d  the  south.  Cut  the  stone  in  two  equal  parts,  and  put  part 
a  in  a.  vessel  and  let  it  float  in  water. 

You  will  find  that  a,  the  north  point,  will  turn  to  the  south 
as  before  ;  and  in  like  manner  the  point  d  will  move  to  the 
north,  in  the  divided  stone,  as  before  division.  But  6  and  c, 
before  connected,  now  separated  from  each  other,  are  not 
what  they  were  before.  3  is  now  south  while  c  is  north. 
d  attracts  c,  longing  for  union  and  for  restoration  of  the 
original  continuity.  They  are  two  stones  made  out  of  one, 
and  on  that  account  the  c  of  one  turning  toward  the  d  of  the 
other,  they  are  mutually  attracted,  and,  being  freed  from  all 
impediments  and  from  their  own  weight,  borne  as  they  are  on 
the  surface  of  the  water,  they  come  together  and  into  con- 
junction. But  if  you  bring  the  part  or  point  a  up  to  c  of  the 
other,  they  repel  one  another  and  turn  away ;  for  by  such  a 
position  of  the  parts  nature  is  crossed  and  the  form  of  the 
stone  is  perverted :  but  nature  observes  strictly  the  laws  it 
has  imposed  upon  bodies:  hence  the  flight  of  one  part  from 
the  undue  position  of  the  other,  and  hence  the  discord  un- 
less everything  is  arranged  exactly  according  to  nature.  And 
nature  will  not  suffer  an  unjust  and  inequitable  peace,  or  an 
unju?^  and  inequitable  peace  and  agreement,  but  makes  war 
and  employs  force  to  make  bodies  acquiesce  fairly  and  justly. 
Hence,  when  rightly  arranged,  the  parts  attract  each  other, 
i.e.,  both  stones,  the  weaker  and  the  stronger,  come  together 
and  with  all  their  might  tend  to  union  :  a  fact  manifest  in  all 
loadstones,  and  not,  as  Pliny  supposed,  only  in  those  from 
Ethiopia.  The  Ethiopic  stones  if  strong,  and  those  brought 
from  China,  which    are   all  powerful   stones,  show  the  effect 


THE  LOADSTONE  ATTRACTS  IRON  ORE.  3 1 

most  quickly  and  most  plainly,  attract  with  most  force  in  the 
parts  nighest  the  pole,  and  keep  turning  till  pole  looks 
straight  on  pole.  The  pole  of  a  stone  has  strongest  attraction 
for  that  part  of  another  stone  which  answers  to  it  (the  adverse 
as  it  is  called) ;  e.g.,  the  north  pole  of  one  has  strongest  attrac- 
tion for,  has  the  most  vigorous  pull  on,  the  south  part  of 
another:  so  too  it  attracts  iron  more  powerfully,  and  iron 
clings  to  it  more  firmly,  whether  previously  magnetized  or 
not.  Thus  it  has  been  settled  by  nature,  not  without  rea- 
son, that  the  parts  nigher  the  pole  shall  have  the  greatest 
attractive  force  ;  and  that  in  the  pole  itself  shall  be  the  seat, 
the  throne  as  it  were,  of  a  high  and  splendid  power ;  and  that 
magnetic  bodies  brought  near  thereto  shall  be  attracted  most 
powerfully  and  relinquished  with  most  reluctance.  So,  too, 
the  poles  are  readiest  to  spurn  and  drive  away  what  is  pre- 
sented to  them  amiss,  and  what  is  inconformable  and 
foreign.* 


CHAPTER  VI. 

THE  LOADSTONE    ATTRACTS   IRON   ORE  AS    WELL  AS    THE 
SMELTED   METAL. 

The  most  potent  virtue  of  the  loadstone  and  the  one^ 
valued  by  the  ancients  is  the  attraction  for  iron ;  for  Plato 
mentions  that  the  magnet,  so  called  by  Euripides,  draws  to 
itself  iron,  and  not  only  attracts  iron  rings  but  also  endows 
them  with  the  power  of  doing  as  the  stone  itself,  to  wit,  of 
attracting  other  rings,  and  that  thus  sometimes  a  long  chain  of 
iron  objects,  as  nails,  or  rings,  is  made,  the  several  parts  hang- 

^  Dr.  J.  Lamont's  "  Handbuch  des  Magnetisniius,"  Leipzig  1867,  page  15. 


32  WILLIAM  GILBERT. 

ing  from  one  another.  The  best  iron  (such  as  that  which 
from  its  uses  is  called  acies,  and  from  the  country  of  the 
Chalybes,  chalybs)  is  most  readily  and  strongly  attracted  by  a 
good  magnet ; '  but  inferior  iron,  iron  that  is  impure,  rusty, 
not  well  purged  of  dross,  and  not  worked  over  in  the  second 
furnace  is  attracted  more  weakly ;  and  any  iron  is  more  faintly 
attracted  if  covered  and  smeared  with  thick,  greasy,  tenacious 
fluids.  The  loadstone  also  attracts  iron  ores— rich  ores  and 
those  of  the  color  of  iron ;  poor  ores  and  those  without  much 
pure  metal  it  does  not  attract  unless  they  receive  special 
treatment.  The  loadstone  loses  some  part  of  its  attractive 
power,  and,  as  it  were,  enters  on  the  decline  of  old  age,  if  it 
be  too  long  exposed  in  open  air  and  not  kept  in  a  case,  with  a 
covering  of  iron  filings  or  iron  scales :  hence  it  must  be  packed 
in  such  material.  Nothing  withstands  this  unimpairable 
virtue,  except  what  destroys  the  form  of  the  body  or  corrodes 
it ;  no,  not  a  thousand  adamants  made  into  one.  Nor  do  I 
believe  in  the  theamedes,  or  that  it  has  a  power  the  opposite  of 
the  loadstone's,'  albeit  Pliny,  that  eminent  author  and  best  of 
compilers  (for  he  has  handed  down  to  posterity  the  observa- 
tions and  discoveries  of  others  and  not  always  or  mainly  his 

1  See  Aristotle's  reference  to  the  iron  of  the  Chalybes  at  page  20.  Dr. 
Thomson  informs  us  the  general  opinion  of  the  ancients  was  that  the  method 
of  smelting  iron  ore  had  been  brought  to  perfection  by  the  Chalybes,  a  small 
nation  located  near  the  Black  Sea  (Xenophon's  Anabasis,  V.  5),  and  that  the 
name  chalybs,  occasionally  used  for  steel,  was  derived  from  that  people.  Porta, 
at  Book  XIII,  Chap.  I,  of  his  "  Natural  Magick,"  says:  "  Justine,  the  historian, 
reports  that  in  Gallicia  of  Spain,  the  chiefest  matter  for  iron  is  found,  ....  and 
there  is  no  weapon  approved  amongst  them  that  is  not  made  of  the  River  Bib- 
ilis,  or  tempered  with  the  water  of  Chalybes.  And  hence  are  those  people  that 
live  neer  this  River  called.  Chalybes;  and  they  are  held  to  have  the  best  iron. 
Yet  Strabo  saith  that  the  Chalybes  were  people  in  Pontus  near  the  River  Ther- 
modon."     See  Gilbert,  Book  I,  Chap.  VIII. 

'■"  "  Iron  is  attracted  by  the  magnet  and  repelled  by  another  stone,  the  the- 
avtddes"  (Pliny,  Hist.  Nat.,  XX,  i).  See,  likewise,  Cardan,  De  Subtil., 
Norimb.  1600,  folio,  Lib.  VII,  page  386. 


WHAT  IRON-  IS;     WHAT  ITS  MATTER;    ITS    USE.         33 

own),  copies  out  of  other  writers  the  theamedes  fable,  now 
from  repetition  become  a  familiar  story  among  the  moderns. 
The  story  is  that  in  India  are  two  mountains  near  the  river 
Indus,  and  that  one  of  them — consisting  of  loadstone — pos- 
sesses the  power  of  holding  everything  containing  iron  ;  while 
the  other,  consisting  of  theamedes,  repels  the  same.  Hence  if 
you  should  have  iron  nails  in  the  soles  of  your  shoes,  it  would 
be  impossible  to  lift  your  foot  if  you  were  standing  on  one  of 
the  mountains,  and  impossible  to  stand  on  the  other  at  all. 
Albertus  Magnus  writes  that  in  his  time  a  loadstone  was  found 
that  on  one  side  drew  iron  to  itself  and  on  the  other  side 
repelled  it.'  But  Albertus's  observation  was  faulty,  for  every 
loadstone  attracts  on  one  side  magnetized  iron,  on  the  other 
repels,  and  attracts  magnetized  iron  more  powerfully  than 
non-magnetized. 


CHAPTER  VII. 

WHAT  IRON    IS;    WHAT   ITS    MATTER;    ITS    USE. 

Having  declared  the  origin  and  nature  of  the  loadstone, 
we  hold  it  needful  first  to  give  the  history  of  iron  also,  and  to 
point  out  properties  of  iron  as  yet  not  known,  before  we  come 
to  the  exphcation  of  difificulties  connected  with  the  loadstone, 

'  Somewhat  in  this  connection,  Gilbert  has  already  (Book  I,  Chap.  I) 
alluded  to  Albertus  Magnus,  of  whom  mention  was  inade  in  note  i,  page  9. 
In  his  De  Miner alibus — Lyons  ed.  1651,  Treat.  Ill,  Lib.  II,  Cap.  VI,  p.  243 — 
Albertus  says,  "  One  angle  ...  is  to  the  zoron  (north),  .  .  .  but  another  angle  of 
the  magnet  opposite  to  it  attracts  to  the  aphron  (south)."  Consult  Cardan,  De 
Subtil.,  Lugduni  1663;  Salmanasar,  Book  II  ("Of  the  Egyptian  Hermitus,  19 
stars,  and  15  stones,  and  15  herbs,  and  15  figures"),  "  On  one  side  (the  magnet) 
attracts  iron,  on  the  other  repels  it;"  Pietro  d'Abano,  Conciliator  Differentia- 
rum  Mantuse,  1472,  Diff.  51,  page  104,  "Know  that  a  magnet  is  discovered 
which  attracts  iron  on  one  side  and  repels  it  on  the  other." 


34  WILLIAM  GILBERT. 

and  to  the  demonstrations ;  before  we  come  to  the  consider- 
ation of  its  uniting  and  according  with  iron.  Iron  is,  by  all, 
classed  among  metals ;  it  is  of  bluish  color,  very  hard,  grows 
red  hot  before  fusion,  is  very  hard  to  fuse,  spreads  under  the 
hammer,  and  is  resonant.  Chemists  say  that,  if  fixed  earthy 
sulphur  be  combined  with  fixed  earthy  mercury  and  these  two 
bodies  present  not  a  pure  white  but  a  bluish-white  color,  if  the 
sulphur  prevail,  iron  results.  For  those  hard  masters  of  the 
metals,  who  in  many  various  processes  put  them  to  the  tor- 
ture, by  crushing,  calcining,  smelting,  subliming,  precipitating, 
distinguish  this,  on  account  both  of  the  earthy  sulphur  and  the 
earthy  mercury,  as  more  truly  the  child  of  earth  than  any 
other  metal ;  for  neither  gold,  nor  silver,  nor  lead,  nor  tin,  nor 
even  copper  do  they  hold  to  be  so  earthy ;  and  therefore  it  is 
treated  only  in  the  hottest  furnaces  with  the  help  of  bellows* 
and  when  thus  smelted  if  it  becomes  hard  again  it  cannot  be 
smelted  once  more  without  great  labor  ;  and  its  slag  can  be 
fused  only  with  the  utmost  difificulty.  It  is  the  hardest  of 
metals,  subduing  and  breaking  them  all,  because  of  the  strong 
concretion  of  the  more  earthy  substance.  Hence  we  shall 
better  understand  what  iron  is  when  we  shall  have  developed, 
in  a  way  different  from  that  of  those  who  have  gone  before  us, 
what  are  the  causes  and  the  matter  of  metals.  Aristotle  sup- 
poses their  matter  to  be  an  exhalation.  The  chemists  in 
chorus  (unison)  declare  that  sulphur  and  quicksilver  are  the 
prime  elements.  Gilgil,  the  Mauretanian,  holds  the  prime  ele- 
ment to  be  ash  moistened  with  water  ;  Georgius  Agricola,  a 
mixture  of  water  with  earth ;  and  his  opinion  differs  nought 
from  Gilgil's  thesis.  But  our  opinion  is  that  metals  have  their 
origin  and  do  effloresce  in  the  uppermost  parts  of  the  globe, 
each  distinct  by  its  form,  as  do  many  other  minerals  and  all 
the  bodies  around  us.     The  globe  of  the  earth  is  not  made  of 


WHAT  IRON  IS;     WHAT  ITS  MATTER ;    ITS   USE.         35 

ash  or  of  inert  dust.  Nor  is  fresh  water  an  element,  but  only 
a  less  complex  consistence  of  the  earth's  evaporated  fluids. 
Unctuous  bodies  {^pinguia  corpora),  fresh  water  void  of  proper- 
ties, quicksilver,  sulphur :  these  are  not  the  principles  of  the 
metals  :  they  are  results  of  another  natural  process ;  nor  have 
they  a  place  now  or  have  they  had  ever,  in  the  process  of 
producing  metals.  The  earth  gives  forth  sundry  humors,  not 
produced  from  water  nor  from  dry  earth,  nor  from  mixtures  of. 
these,  but  from  the  matter  of  the  earth  itself :  these  are  not 
distinguished  by  opposite  qualities  or  substances.  Nor  is  the 
earth  a  simple  substance,  as  the  Peripatetics  imagine.  The 
humors  come  from  sublimed  vapors  that  have  their  origin  in 
the  bowels  of  the  earth.  And  all  waters  are  extractions  from 
the  earth  and  exudations,  as  it  were.  Therefore  Aristotle  is 
partly  in  the  right  when  he  says  that  the  exhalation  which 
condenses  in  the  earth's  veins  is  the  prime  matter  of  metals : 
for  exhalations  are  condensed  in  situations  less  warm  than  the 
place  of  their  origin,  and  owing  to  the  structure  of  lands  and 
mountains,  they  are  in  due  time  condensed,  as  it  were,  in 
wombs,  and  changed  into  metals.  But  they  do  not  of  them- 
selves alone  constitute  the  veins  of  ore ;  only  they  flow  into 
and  coalesce  with  solider  matter  and  form  metals.  When, 
therefore,  this  concreted  matter  has  settled  in  more  temperate 
cavities,  in  these  moderately  warm  spaces  it  takes  shape,  just 
as  in  the  warm  uterus  the  seed  or  the  embryo  grows.  Some- 
times the  exhalation  coalesces  only  with  matter  homogene- 
ous throughout,  and  hence  some  metals  are  now  and  then 
but  not  often  obtained  pure  and  not  needing  to  be  smelted. 
But  other  exhalations,  being  mixed  with  foreign  earths,  must 
be  smelted ;  and  thus  are  treated  the  ores  of  all  metals,  which 
are  freed  from  all  their  dross  by  the  action  of  fire  ;  when  smelted 
into  the  metallic  state  they  are  fluid  and  then  are  freed  from 


36  WILLIAM  GILBERT. 

earthly  impurities  but  not  from  the  true  substance  of  the  earth. 
But  that  there  is  gold,  or  silver,  or  copper,  or  that  any  other 
metals  exist,  does  not  happen  from  any  quantitas  or  propor- 
tion of  matter  nor  by  any  specific  virtues  of  matter,  as  the 
chemists  fondly  imagine ;  but  it  happens  when,  earth  cavities 
and  the  conformation  of  the  ground  concurring  with  the  fit 
matter,  those  metals  take  from  universal  nature  the  forms  by 
which  they  are  perfected,  just  as  in  the  case  of  all  other  min- 
erals, all  plants  and  all  animals :  else  the  kinds  of  metals  would 
be  vague  and  undefined :  in  fact  the  varieties  are  very  few^ 
hardly  ten  in  number.  But  why  nature  should  be  so  grudging 
in  the  number  of  metals,  or  why  there  should  be  even  so  many 
metals  as  are  recognized  by  man,  were  not  easy  to  explain, 
though  simpletons  and  raving  astrologers  refer  to  the  several 
planets  their  respective  metals.'  But  neither  do  the  planets 
agree  with  the  metals  nor  the  metals  with  the  planets,  either 
in  number  or  in  properties.  For  what  is  common  be- 
tween Mars  and  iron,  save  that,  like  many  other  implements, 
swords  and  artillery  are  made  of  iron  ?  What  has  copper  to 
do  with  Venus?  Or  how  does  tin,  or  zinc,  relate  to  Jupiter? 
These  were  better  dedicated  to  Venus.  But  a  truce  to  old 
wives'  talk.  Thus  exhalations  are  the  remote  cause  of  the 
generation  of  metals ;  the  proximate  cause  is  the  fluid  from  the 
exhalations  :  like  the  blood  and  the  semen  in  the  generation  of 
animals.     But  these  exhalations  and  the  fluids  produced  from 

'  In  his  account  of  Geber  (Abou-Moussah-Dschafar-Al-Soli),  "  the  patri- 
arch of  chemistry,"  Dr.  Thos.  Thomson  says  this  Arabian  philosopher  was 
acquainted  with  the  metals  gold,  silver,  copper,  iron,  tin,  and  lead,  and  that  they 
are  usually  distinguished  by  him  under  the  respective  names  of  Sol,  Luna, 
Venus,  Mars,  Jupiter,  and  Saturn.  He  adds  :  "Whether  these  names  of  the 
planets  were  applied  to  the  metals  by  Geber,  or  only  by  his  translators,  I  can- 
not say;  but  they  were  always  employed  by  the  Alchy mists,  who  never  desig- 
nated the  metals  by  any  other  appellations"  ("Hist,  of  Chem.",  1830,  Vol.  I, 
pages  117,  118). 


WHAT  IRON  IS;     WHAT  ITS  MATTER;    ITS    USE.         37 

them  enter  bodies  often  and  change  them  into  marchasites' 
and  they  pass  into  veins  (we  find  many  instances  of  timber  so 
transformed),  into  appropriate  matrices  within  bodies,  and  these 
metals  are  formed  ;  oftenest  they  enter  the  more  interior  and 
more  homogeneous  matter  of  the  globe,  and  in  time  there  re- 
sults a  vein  of  iron,  or  loadstone  is  produced,  which  is  nothing 
but  a  noble  iron  ore  ;  and  for  this  reason  and  also  on  account 
of  its  matter  being  quite  pecuhar  and  distinct  from  that  of  all 
other  metals,  nature  very  seldom  or  never  mingles  with  iron  any 
other  metal,  though  the  other  metals  are  very  often  commin- 
gled in  some  small  proportion  and  are  produced  together. 
Now,  when  these  exhalations  or  fluids  happen  to  meet  efflo- 
rescences altered  from  the  homogeneous  matter  of  the  globe — 
sundry  precipitates,  and  salts,  in  suitable  matrices  (operant 
forms) — the  other  metals  are  produced  (a  specificating  nature 
operating  in  that  place).  For  within  the  globe  are  hidden  the 
principles  of  metals  and  stones,  as  at  the  earth's  surface  are 
hidden  the  principles  of  herbs  and  plants.  And  earth  dug  from 
the  bottom  of  a  deep  pit,  where  there  appears  to  be  no  chance 
of  any  seed  being  formed,  produces,  if  strewn  on  the  top  of  a 
very  high  tower,  green  herbage  and  unbidden  grasses,  the  sun 
and  the  sky  brooding  over  earth ;  the  earth  regions  produce 
those  things  which  in  each  are  spontaneous  ;  each  region  pro- 
duces its  own  peculiar  herbs  and  plants,  its  own  metals. 

Do  you  not  see  how  Tmolus  sends  fragrant  saflfron,  India  its  ivory, 
the  Sabaens  their  frankincense,  the  naked  Chalybes  iron,  Pontus  the 
malodorous  castor,  Epirus  the  mares  that  have  won  at  Olympia? 
(Virgil ius,  Georgica,  Book  I,  pages  56-59.) 

'  Marchasites,  marcasites — the  crystallized  form  of  iron  pyrites.  What 
substance  Geber  designated  by  the  name  cf  marchasite  (fire-stone,  as  Porta 
calls  it — "  Nat.  Magick,"  Book  V,  Chap.  IV)  is  not  known  to  Dr.  Thomson,  who 
suspects  it  to  have  been  a  sulphide  of  antimony  long  in  common  use  through- 
out Asia. 


38  WILLIAM  GILBERT. 

What  the  chemists  (as  Geber  and  others)  call  the  fixed 
earthy  sulphur  in  iron,  is  nothing  else  but  the  homogenic  mat- 
ter of  the  globe  held  together  by  its  own  humor,  hardened  by 
a  second  humor  :  with  a  minute  quantity  of  earth-substance  not 
lacking  humor  is  introduced  the  metallic  humor.  Hence  it  is 
said  very  incorrectly  by  many  authors  that  in  gold  is  pure 
earth,  in  iron  impure ;  as  though  natural  earth  and  the  globe 
itself  were  become  in  some  incomprehensible  sense  impure.  In 
iron,  especially  in  best  iron,  is  earth  in  its  true  and  genuine 
nature.  In  the  other  metals  is  not  so  much  earth  as,  instead 
of  earth  and  precipitate,  condensed  and  (so  to  speak)  fixed 
salts,  which  are  efiflorescences  of  the  Earth,  and  which  also  dif- 
fer in  firmness  and  consistence.  In  mines  they  ascend  in  great 
volume,  with  double  humor  from  the  exhalations ;  in  the  sub- 
terranean spaces  they  are  consolidated  into  metallic  ores ;  so 
too  they  are  produced  together,  and  in  virtue  of  their  place 
and  of  the  surrounding  bodies,  they  acquire,  in  natural  matrices, 
their  specific  forms.  Of  the  various  bodily  constitutions  of 
loadstones,  their  different  substances,  colors,  and  properties, 
we  have  spoken  before :  but  now  after  having  declared  the 
cause  and  origin  of  metals,  the  matter  of  iron,  not  in  the  smelted 
metal  but  in  the  ore  from  which  that  is  obtained  by  smelting, 
has  to  be  examined.  Iron,  that  from  its  color  appears  pure,  is 
found  in  the  earth  ;  yet  it  is  not  exactly  metallic  iron,  not 
quite  suitable  for  the  different  uses  of  iron.  Sometimes  it  is 
found  covered  with  a  white  moss-like  substance,  or  with  a  coat- 
ing of  other  stones.  Such  ore  is  often  seen  in  the  sands  of 
rivers :  such  is  the  ore  from  Noricum  (the  region  south  of 
the  Danube,  watered  by  the  Inn  \CEnus\  and  the  Drave  \Drau\  ; 
mostly  comprised  in  the  modern  Austria).  Iron  ore,  nearly 
pure,  is  often  mined  in  Ireland :  from  this  the  smith,  without 
the  labor  of  the  furnace,  forges  in  his  shop  iron  implements. 


WHAT  IRON  IS;     WHAT  ITS  MATTER;    ITS   USE.         39 

From  an  ore  of  liver  color  is  very  often  obtained  in  France  an 
iron  with  bright  scales  {bractecs) ' ;  such  iron  is  made  in  England 
without  the  scales  ;  carpenters  use  it  instead  of  chalk.  In  Sus- 
sex, in  England,  is  a  rich  ore  of  dark,  and  one  of  pale  ashy 
color ;  both  of  these  ores  when  made  red  hot  for  some  time, 
or  when  kept  in  a  moderate  fire,  take  the  color  of  liver :  in 
Sussex  also  is  a  dark-colored  ore  in  square  masses,  with  a  black 
rind  of  harder  material.  The  liver-like  ore  is  often  mixed  with 
other  stones  in  various  ways,  as  also  with  perfect  loadstone, 
which  yields  the  best  iron.  There  is  likewise  rust-colored  ore, 
ore  of  a  lead  color  mixed  with  black,  simply  black,  or  black 
mixed  with  cobalt ;  there  is  also  an  ore  with  admixture  of 
pyrites  or  sterile  plumbago.  One  kind  of  ore  resembles  jet, 
another  the  precious  stone  hcematites.  The  stone  smiris 
(emery ;  corundum)  used  by  workers  in  glass  for  glass-cutting 
and  called  by  the  English  emerelstone  and  by  the  Germans 
smear  gel  (schniergel),  is  of  iron,  albeit  iron  is  smelted  from  it 
with  difficulty  ;  it  attracts  an  unmagnetized  needle.  It  is  often 
found  in  deep  silver  and  iron  mines.  Thomas  Erastus  tells  of 
having  been  informed  by  a  certain  learned  man,  of  iron  ores, 
in  color  resembling  metallic  iron,  but  quite  soft  and  greasy, 
capable  of  being  moulded  with  the  fingers  like  butter  ;  we  have 
seen  ores  of  about  the  same  kind  that  were  found  in  England  : 
they  resemble  Spanish  soap.  Besides  the  numberless  forms  of 
stony  ores,  there  is  a  substance  like  iron  rust  deposited  from 
ferriferous  water :  it  is  got  from  mud,  loam,  and  from  ochre. 
In  England,  a  good  deal  of  iron  is  obtained  in  the  furnace  from 


1  At  page  280,  Vol.  I,  of  Thomson's  "Hist,  of  Chem.",  London  1830, 
will  be  found  an  account  of  the  difficulty  experienced  by  Reaumur  in  removing 
the  scales  from  the  iron  imported  from  Germany  into  France.  Elsewhere,  he 
tells  us  that  the  rust  of  iron  and  the  scales  of  iron  were  used  by  the  ancients  as 
astringent  medicines.     See  note  at  Book  II,  Chap.  XXIII,  of  the  present  work. 


40  WILLIAM  GILBERT. 

sand  stones  and  clayey  stones  that  appear  to  contain  not  so 
much  iron  as  sand,  marl,  or  other  mud.  In  Aristotle's  book 
De  Adniirandis  Narrationibus  we  read  : 

'Tis  said  the  iron  of  the  Chalybes  and  the  Myseni  has 
quite  a  peculiar  origin,  being  carried  in  the  gravel  of  the 
streams.  Some  say  that,  after  being  merely  washed,  it  is 
smelted  in  the  furnace  ;  others  that  is  washed  repeatedly,  and 
as  often  the  residue  treated  with  fire  in  the  furnace,  together 
with  the  stone  pyrimachus  (a  stone  refractory  to  the  action  of 
fire),  which  occurs  there  in  great  abundance.  Thus  do  many 
sorts  of  substances  contain  in  themselves  strikingly  and  most 
plentifully  this  ferric  and  telluric  element.  Many,  too,  and 
most  plentiful  in  every  soil  are  the  stones  and  earths  and  the 
various  bodies  and  compounds,  which  contain  iron  (though  not 
in  such  abundance)  and  yield  it  in  the  furnace  fire,  but  which 
are  rejected  by  the  metallurgist  as  not  workable  with  profit ; 
and  there  are  other  earths  that  give  evidence  of  the  presence 
of  iron  in  them ;  these,  being  very  poor  in  the  metal,  are  not 
smelted  at  all,  and  not  being  esteemed  they  are  not  known. 

The  kinds  of  manufactured  iron  differ  very  much  from  one 
another.  For  one  kind  has  great  tenacity ;  and  that  is  the 
best.  There  is  a  medium  kind.  Another  kind  is  brittle ; 
that  is  the  worst.  Sometimes  the  iron,  on  account  of  the  ex- 
cellence of  the  ore,  is  made  into  steel ;  as  in  Noricum  at  present. 
From  the  best  iron  also,  worked  over  and  over  again,  and  purged 
of  all  impurities,  or  plunged  red-hot  into  water,  is  produced 
what  the  Greeks  call  Gtojxwfxa^  and  the  Latins  acies  and 
aciarium  (steel),  and  which  is  variously  called  Syrian,  Parthian, 


1  Stomoma  was  also  the  name  given  to  an  oxide  of  copper,  which  was 
gradually  formed  upon  the  surface  of  metal,  when  it  was  kept  in  a  state  of 
fusion.  Such  oxides  of  copper  were  used  as  external  applications,  seemingly 
as  escharotics  (Dr.  Thomson's  Chemistry,  1830,  Vol.  I,  page  60). 


WHAT  IRON  IS;     WHAT  ITS  MATTER;    ITS    USE.        41 

Norican,  Comese  and  Spanish  ;  in  other  places  it  takes  its  name 
from  the  water  in  which  it  is  repeatedly  immersed,  as  at  Como 
in  Italy,  and  Bilbao  and  Tariassone  in  Spain.  Steel  sells  at  a 
far  higher  price  than  iron.  And,  on  account  of  its  superiority, 
it  is  in  better  accord  with  the  magnet.  It  is  often  made  from 
powerful  loadstone,  and  it  acquires  the  magnetic  virtue  readily, 
retains  it  a  long  time  unimpaired  and  fit  for  all  magnetic  ex- 
periments. 

The  iron,  after  it  has  been  smelted  in  the  first  furnace,  is 
then  treated  with  various  processes  in  great  forges  or  mills,  the 
metal  under  mighty  blows  acquiring  toughness,  and  dropping 
its  impurities.  When  first  smelted  it  is  brittle  and  by  no  means 
perfect.  Therefore,  here  in  England,  when  great  cannons  are 
cast,  in  order  that  they  may  be  able  to  withstand  the  explo- 
sive force  of  the  ignited  gunpowder,  the  metal  is  specially 
purged  of  impurities :  while  fluid  it  is  made  to  pass  a  second 
time  through  a  narrow  opening,  and  thus  is  freed  of  recre- 
mental  substances.  Smiths,  with  the  use  of  certain  liquids  and 
hammer-strokes,  toughen  the  iron  laminae  from  which  are  made 
shields  and  coats  of  mail  not  penetrable  by  any  musket-ball. 
Iron  is  made  harder  by  skill  and  tempering;  but  skill  also 
makes  it  softer  and  as  pliant  as  lead.  It  is  made  hard  by  cer- 
tain waters  into  which  it  is  plunged  at  white  heat,  as  in  Spain. 
It  is  made  soft  again  either  by  fire  alone  when,  without  ham- 
mering and  without  the  use  of  water,  it  is  allowed  to  grow 
cool ;  or  by  being  dipped  in  grease  ;  or  it  is  variously  tempered, 
to  serve  the  purposes  of  the  different  arts,  by  being  smeared 
with  special  preparations.  This  art  is  described  by  Baptista 
Porta  in  book  13  of  the  Magia  Naturalis. 

Thus  is  this  ferric  and  telluric  substance  contained  in  and 
extracted  from  various  kinds  of  stones,  ores,  and  earths ; 
thus  too  does  it  differ  in  appearance,  form,  and  efficiency ;  and 


42  WILLIAM  GILBERT. 

by  various  processes  of  art  it  is  smelted  and  purified  and  made 
to  serve  man's  uses  in  all  sorts  of  trades  and  in  all  sorts  of  tools, 
as  no  other  body  can  serve.  One  kind  of  iron  is  suitable  for 
breastplates,  another  withstands  cannon  balls,  another  pro- 
tects against  swords  or  the  curved  blades  called  cimetars ;  one 
kind  is  used  in  making  swords,  another  in  forging  horseshoes. 
Of  iron  are  made  nails,  hinges,  bolts,  saws,  keys,  bars,  doors, 
folding-doors,  spades,  rods,  pitchforks,  heckles,  hooks,  fish- 
spears,  pots,  tripods,  anvils,  hammers,  wedges,  chains,  manacles 
fetters,  hoes,  mattocks,  sickles,  hooks  for  pruning  vines  and, 
for  cutting  rushes  {scirpiculcE),  shovels,  hoes,  weeding-hooks, 
ploughshares,  forks,  pans,  ladles,  spoons,  roasting-spits,  knives, 
daggers,  swords,  axes,  Celtic  and  Gallic  darts  {gesscs),  Mace- 
donian pikes  {sarisscB)^  lances,  spears,  anchors  and  many  nauti- 
cal implements ;  furthermore,  bullets,  javelins,  pikes,  corselets, 
helmets,  breastplates,  horseshoes,  greaves,  wire,  strings  of  mu- 
sical instruments,  armchairs,  portcullises,  bows,  catapults,  and 
those  pests  of  humanity,  bombs,  muskets,  cannon-balls,  and 
no  end  of  implements  unknown  to  the  Latins.  I  have  re- 
counted so  many  uses  in  order  that  the  reader  may  know  in 
how  many  ways  this  metal  is  employed.  Its  use  exceeds  that 
of  all  other  metals  a  hundredfold ;  it  is  smelted  daily ;  and 
there  are  in  every  village  iron  forges.  For  iron  is  foremost 
among  metals  and  supplies  many  human  needs,  and  they  the 
most  pressing :  it  is  also  far  more  abundant  in  the  earth  than 
the  other  metals,  and  it  is  predominant.  Therefore  it  is  a  vain 
imagination  of  chemists  to  deem  that  nature's  purpose  is  to 
change  all  metals  to  gold,  that  being  brightest,  heaviest,  strong- 
est, as  though  she  were  invulnerable,  would  change  all  stones 
into  diamonds  because  the  diamond  surpasses  them  all  in 
brilliancy  and  in  hardness.  Iron  ore,  therefore,  as  also  manu- 
factured iron,  is  a  metal  slightly  different  from  the  primordial 


//V    WHAT  COUNTRIES  IRON  IS  PRODUCED.  43 

homogenic  telluric  body  because  of  the  metallic  humor  it  has 
imbibed ;  yet  not  so  different  but  that  in  proportion  as  it  is 
purified  it  takes  in  more  and  more  of  the  magnetic  virtues,  and 
associates  itself  with  that  prepotent  form  and  duly  obeys  the 
same. 


CHAPTER  VIII. 

IN  WHAT  COUNTRIES  AND  REGIONS  IRON   IS   PRODUCED. 

Iron   mines    are   very   numerous    everywhere — both    the 
ancient  mines  mentioned  by  the  earliest  writers  and  the  new 
and  modern   ones.     The  first  and  greatest  were,  I    think,  in 
Asia,  for  in  the  countries  of  Asia,  which  naturally  abound  in 
iron,  government  and  the  arts  did  most  flourish ;    and  there 
were  the  things  needful  for  man's  use    first  discovered    and 
sought  for.     It  is  related  that  iron  existed  in  the  neighborhood 
of  Andria ;    in  the  land  of  the  Chalybes,  on   the  banks  of  the 
river  Thermodon  in   Pontus ;    in  the  mountains  of  Palestine 
on  the  side  toward  Arabia ;   in   Carmania.     In  Africa,  there 
was  an  iron  mine  in  the  island  of  Meroe.     In  Europe,  iron  was 
found  in  the  hills  of  Britain,  as  Strabo  writes  ;  in  hither  Spain, 
in  Cantabria ;  among  the  Petrocorii  and  the  Cabi  Bituriges  in 
Gaul,  were  smithies  in  which  iron  was  made.     In  Germany  was 
a  mine  near  Luna,  mentioned  by  Ptolemy  ;  the  Gothinian  iron 
is  spoken  of  by  Cornelius  Tacitus ;  and  the  iron  of  Noricum  is 
famed  in  poesy ;   there  was  also  iron  in  Crete  and  in  Euboea. 
Many  other  mines,  neither  meagre  nor  scant,  but  of  vast  ex- 
tent, were  overlooked  by  writers  or  were  unknown  to  them. 
Pliny  calls  hither  Spain  and  the  whole  region  of  the  Pyrenees 


44  WILLIAM  GILBERT. 

an  iron  country;  and  he  says  that,  in  the  part  of  Cantabria 
washed  by  the  ocean,  there  is  a  mountain  steep  and  high  which 
(wonderful  to  tell)  is  all  iron.  The  earliest  mines  were  iron 
mines,  not  mines  of  gold,  silver,  copper  or  lead  :  for  iron  is 
more  sought  after  for  the  needs  of  man  ;  besides,  iron  mines 
are  plainly  visible  in  every  country,  in  every  soil,  and  they  are 
less  deep  and  less  encompassed  with  difficulties  than  other 
mines.  But  were  I  simply  to  enumerate  modern  iron  mines 
and  those  worked  in  our  own  time,  a  very  'large  book  would 
have  to  be  written,  and  paper  would  fail  me  before  iron :  yet 
each  one  of  these  mines  could  supply  looo  forges.  For  among 
minerals  there  is  no  other  substance  so  plentiful :  all  metals 
and  all  stones  distinct  from  iron  ore  are  surpassed  by  ferric  and 
ferruginous  substances.  For  you  cannot  easily  find  a  district, 
hardly  a  township,  throughout  all  Europe,  if  you  search 
thoroughly,  that  has  not  a  rich  and  plentiful  vein  of  iron,  or 
that  does  not  yield  an  earth  either  saturated  with  iron-rust  or 
at  least  slightly  tinctured  with  it.  That  this  is  so,  is  easily  shown 
by  any  one  versed  in  metallurgy  and  chemistry. 

Besides  iron  and  its  ore,  there  is  another  ferric  substance, 
which,  however,  does  not  yield  the  metal,  because  the  thin 
humor  is  burnt  up  by  the  fierce  fires  and  is  converted  into  dross 
like  that  separated  from  the  metal  when  first  smelted.  Such 
is  the  white  clay  and  argillaceous  earth  which  is  seen  to  make 
up  great  part  of  our  British  island  ;  this,  if  treated  with  strong 
heat,  either  exhibits  a  ferric  and  metallic  body,  or  is  trans- 
formed into  a  ferric  vitrification  :  this  fact  can  be  verified  in 
houses  built  of  brick,  for  the  bricks  that  in  the  kiln  are  laid 
nearest  to  the  fires,  and  are  there  burnt,  show  ferric  vitrifica- 
tion at  their  other  end,  which  grows  black.  Furthermore,  all 
those  earths  when  prepared,  are  attracted  by  the  magnet  like 
iron.     Lasting  and   plentiful   is  the  earth's  product  of  iron. 


IN    WHAT  COUNTRIES  IRON  IS  PRODUCED.  45 

Georgius  Agricola  says  that  nearly  all  mountainous  regions  are 
full  of  its  ores ;  and  we,  ourselves,  do  know  that  a  rich  iron  ore 
is  often  dug  in  the  lowlands  and  plains  throughout  England 
and  Ireland,  as  Agricola  tells  of  iron  being  dug  in  the  meadows 
near  the  town  of  Saga'  out  of  ditches  not  more  than  two  feet 
deep.  Nor  is  iron  lacking,  as  some  say,  in  the  West  Indies ; 
but,  there,  the  Spaniards,  intent  on  gold,  avoid  the  toilsome 
manufacture  of  iron  and  do  not  search  for  rich  iron  ores  and 
mines.  It  is  probable  that  nature  and  the  terrestrial  globe 
cannot  repress,  but  is  ever  sending  forth  into  the  light  a  great 
quantity  of  its  own  native  substance,  and  that  this  action  is  not 
entirely  impeded  by  the  pressure  of  the  mingled  substances 
and  efflorescences  at  the  circumference.  But  iron  is  produced 
not  only  in  the  common  mother  (the  globe  of  Earth),  but 
sometimes  is  also  in  the  air,  in  the  uppermost  clouds  from  the 
earth's  vapors.  It  rained  iron  in  Lucania  the  year  that  Marcus 
Crassus  met  his  death.  They  tell,  too,  of  a  mass  of  iron,  re- 
sembling slag,  having  fallen  out  of  the  air  in  the  Nethorian 
forest  near  Grina,  which  is  said  to  have  weighed  several 
pounds ;  and  that  it  could  not  be  carried  to  that  village  it  was 
so  heavy,  and  could  not  be  taken  on  a  wagon  because  there 
were  no  roads.  This  happened  before  the  Civil  War  of  the 
Saxons,  waged  by  the  Dukes.  A  similar  occurrence  is  men- 
tioned by  Avicenna.  In  the  Torinese,  it  once  rained  iron  at 
several  points,  some  three  years  before  that  province  was  con- 
quered by  the  King.     In  the  year  1510,  as  Cardan  relates  in 


•  "The  like  wee  reade  of  at  Saga  in  Ligys,  where  they  digge  over  their 
iron  mines  every  tenth  yeare.  .  .  .  But  whosoever  readeth  that  which  Francis 
Leandro  hath  written  touching  the  iron  mineralls  in  the  He  of  Elba,  will  cleave 
perhaps  to  a  third  conceit,  for  he  avoucheth  that  the  trenches  out  of  which  the 
oare  there  is  digged,  within  twenty  or  thirty  yeares,  become  alike  full  a.^aine 
of  the  same  mettall  as  at  first "  (Geo.  Hakewill's  "  Apologie,"  1635,  Lib.  II, 
Sec.  7,  pages  164-165). 


4^  WILLIAM  GILBERT. 

his  book  De  Rerum  Varietate,  there  fell  from  the  sky,  upon  a 
field  near  the  river  Abdua,  1200  stones,  one  of  which  weighed 
120,  another  30  or  40,  pounds,  all  of  them  the  color  of  iron  and 
exceedingly  hard.  These  occurrences,  because  they  happen 
seldom,  seem  to  be  portents,  like  the  earth-rains  and  stone- 
showers  mentioned  in  the  annals  of  the  Romans.  But  that  it 
ever  rained  other  metals  is  not  mentioned  ;  for  it  does  not  ap- 
pear that  gold,  silver,  lead,  tin,  or  zinc  ever  fell  from  heaven. 
But  copper  has  sometimes  been  observed  to  fall  from  the 
clouds — a  metal  differing  not  much  from  iron :  and  this  cloud- 
gendered  iron  and  copper  are  seen  to  be  imperfect  metals,  ab- 
solutely infusible  and  unforgeable.  For  the  earth,  in  its  emi- 
nences, abounds  in  store  of  iron,  and  the  globe  contains  great 
plenty  of  ferric  and  magnetic  matter.  Exhalations  of  such 
matter  sent  forth  with  some  violence  may,  with  the  concur- 
rence of  powerful  agencies,  become  condensed  in  the  upper 
regions,  and  so  may  be  evolved  a  certain  monstrous  progeny 
of  iron. 


CHAPTER  IX. 

IRON   ORE   ATTRACTS   IRON   ORE. 

Like  the  other  metals,  iron  is  obtained  from  various  sub- 
stances— stones,  earths,  and  such-like  concretions,  called  by 
miners  ores,  or  veins,  because  they  are  produced  in  fissures 
of  the  earth.  Of  the  diversity  of  ores  we  have  already  spoken. 
A  piece  of  crude  iron  ore  of  the  color  of  iron  and  rich,  as 
miners  say,  when  floated  in  a  bowl  or  other  vessel  in  water  (as 
in  the  case  of  the  loadstone  supra)  is  usually  attracted  by  a 


IRON  ORE  HAS  AND  ACQUIRES  POLES.  4/ 

like  piece  of  ore  held  in  the  hand  and  brought  near  to  it,  but 
it  is  not  attracted  strongly  and  with  rapidity  as  a  loadstone  is 
drawn  by  a  loadstone,  but  slowly  and  weakly.  Stony  ores, 
and  those  of  an  ashy,  brown,  ruddy,  etc.,  color,  neither  attract 
one  another  nor  are  attracted  even  by  a  powerful  loadstone, 
any  more  than  so  much  wood  or  lead  or  silver  or  gold  would  be. 
Take  some  pieces  of  such  ores  and  roast  or  rather  heat  them 
in  a  moderate  fire  so  that  they  may  not  suddenly  split  or  fly  to 
pieces,  and  retain  them  ten  or  twelve  hours  in  the  fire,  which 
is  to  be  kept  up  and  moderately  increased  ;  then  suffer  them 
to  cool,  according  to  the  method  given  in  Book  III,  Of  Direc- 
tion :  these  stones  so  manipulated,  the  loadstone  now  attracts ; 
they  show  mutual  sympathy,  and,  when  arranged  according  to 
artificial  conditions,  they  come  together  through  the  action  of 
their  own  forces. 


CHAPTER   X. 

IRON  ORE  HAS  AND  ACQUIRES  POLES,  AND  ARRANGES  ITSELF 
WITH  REFERENCE  TO  THE  EARTH'S  POLES. 

Men  are  deplorably  ignorant  with  respect  to  natural  things,  :?• 
and  modern  philosophers,  as  though  dreaming  in  the  darkness, 
must  be  aroused  and  taught  the  uses  of  things,  the  dealing 
with  things ;  they  must  be  made  to  quit  the  sort  of  learning 
that  comes  only  from  books,  and  that  rests  only  on  vain  argu- 
ments from  probability  and  upon  conjectures.  For  the  science 
of  iron  (than  which  nought  is  more  in  use  among  us),  as  of 
many  other  bodies,  remains  unknown — iron,  I  say,  whose  rich 
ore,  by  an  inborn  force,  when  floated  in  a  vessel  on  water,  as- 


48  WILLIAM  GILBERT. 

sumes,  like  the  loadstone,  a  north  and  south  direction,  coming 
to  a  standstill  at  those  points,  whence  if  it  be  turned  away,  it 
goes  back  to  them  again  in  virtue  of  its  inborn  activity.  But 
of  less  perfect  ores  which,  however,  under  the  guise  of  stone 
or  earth  contain  a  good  deal  of  iron,  few  possess  the  power  of 
movement ;  yet  when  treated  artificially  with  fire,  as  told  in  the 
foregoing  chapter,  these  acquire  polar  activity,strength  {verticity, 
as  we  call  it) ;  and  not  only  such  ores  as  miners  seek,  but  even 
earths  simply  impregnated  with  ferruginous  matter,  and  many 
kinds  of  rock,  do  in  like  manner  (provided  they  be  skilfully 
placed),  tend  and  glide  toward  those  positions  of  the  heavens, 
or  rather  of  the  earth,  until  they  reach  the  point  they  are 
seeking :  there  they  eagerly  rest. 


CHAPTER  XL 

WROUGHT-IRON,  NOT   MAGNETIZED   BY   THE   LOADSTONE, 
ATTRACTS  IRON. 

*  Iron  is  extracted  in  the  first  furnace  from  the  ore,  which  is 
converted  or  separated  partly  into  metal,  partly  into  dross,  by 
the  action  of  very  great  heat  continued  for  eight,  ten,  or  twelve 
hours.  The  metal  flows  out,  leaving  behind  the  dross  and  use- 
less substances,  and  forms  a  great  long  mass,  which  under  the 
blows  of  a  large  hammer  is  cut  into  pieces :  from  these,  after 
being  reduced  in  another  furnace  and  again  put  on  the  anvil, 
the  workmen  form  cubical  masses,  or  more  usually  bars,  which 
are  sold  to  merchants  and  blacksmiths :  from  these  blocks  or 
bars  are  everywhere  made  in  smiths'  shops  various  implements. 


WROUGHT-IRON,   NOT  MAGNETIZED,  ATTRACTS  IRoN.       49 

This  we  call  wrought-iron,  and,  as  every  one  knows,  it  is  at- 
tracted by  the  loadstone.  But  we,  steadily  trying  all  sorts  of 
experiments,  have  discovered  that  mere  iron  itself,  magnetized 
by  no  loadstone,  nor  impregnated  with  any  extraneous  force, 
attracts  other  iron,  though  it  does  not  seize  the  other  iron  as 
eagerly  nor  as  suddenly  pulls  it  to  itself  as  would  a  strong 
loadstone.  That  this  is  so  you  may  learn  from  the  following 
experiment :  A  small  piece  of  cork,  round,  and  the  size  of  a 
filbert,  has  an  iron  wire  passed  through  it  to  the  middle 
of  the  wire :  float  this  in  still  water  and  approach  (without 
contact)  to  one  end  of  that  wire,  the  end  of  another  wire : 
wire  attracts  wire,  and  when  the  one  is  withdrawn  slowly  the 
other  follov/s,  yet  this  action  takes  place  only  within  fit  limits. 
In  the  figure,  A  is  the  cork  holding  the  wire,  B  one  end  of  the 


wire  rising  a  little  out  of  the  water,  C  the  end  of  the  second 
wire,  which  pulls  B.  You  may  demonstrate  the  same  thing 
with  a  larger  mass  of  iron.  Suspend  in  equilibrium  with  a 
slender  silken  cord  a  long  rod  of  polished  iron,  such  as  are  used 
to  support  hangings  and  curtains  ;  bring  within  the  distance  of 
half  a  finger's  length  of  one  end  of  this  as  it  rests  still  in  the 
air,  some  oblong  mass  of  polished  iron  with  suitable  end  :  the 
balanced  rod  returns  to  the  mass :  then  quickly  withdraw 
your  hand  with  the  mass  in  a  circular  track  around  the  point 
of  equilibrium  of  the  suspended  rod,  and  the  cord  holding  the 
rod  will  travel  in  a  circle. 


so  WILLIAM  GILBERT. 


CHAPTER    XII. 

A  LONG  PIECE  OF  IRON,  EVEN  NOT  MAGNETIZED,  ASSUMES  A 
NORTH   AND   SOUTH   DIRECTION. 

I  All  good  and  perfect  iron,  if  it  be  drawn  out  long,  acts 
like  a  loadstone  or  like  iron  rubbed  with  loadstone :  it  takes  the 
direction  north  and  south — a  thing  not  at  all  understood  by 
our  great  philosophers  who  have  labored  in  vain  to  demon- 
strate the  properties  of  the  loadstone  and  the  causes  of  the 
friendship  of  iron  for  the  loadstone.  Experiment  can  be  made 
either  with  large  or  small  objects  of  iron,  either  in  air  or  in 
water.  A  straight  rod  of  iron  six  feet  in  length  and  as  thick 
as  one's  finger  is  (as  described  in  the  foregoing  chapter)  sus- 
pended in  exact  equilibrium  with  a  fine  but  strong  silk  thread. 
The  thread,  however,  should  be  composed  of  several  silk  fila- 
ments, twisted  differently  and  not  all  in  one  direction.  Let  the 
experiment  be  made  in  a  small  room  with  doors  and  windows  all 
closed,  to  prevent  currents  of  air  in  the  room :  hence  it  is  not 
well  to  experiment  on  windy  days  or  when  a  storm  is  brewing. 
The  rod  of  iron  freely  acts  according  to  its  property  and  moves 
slowly  until  at  last  coming  to  a  stop  at  its  goals  it  points  north 
and  south,  like  magnetized  iron  in  a  sun-dial,  a  common  mag- 
netic compass,  and  the  mariner's  compass.  You  may,  if  you 
are  curious  of  such  experiments,  suspend  at  once  from  slender 
threads,  iron  rods,  or  wires,  or  knitting-needles :  you  shall  find 
them  all  in  accord  unless  there  is  some  flaw  in  the  conduct  of 
this  interesting  experiment;  for  unless  you  make  all  the 
preparations  precisely  and    exactly,  your   labor  will  be  vain. 


FIXED  NORTH  AND   SOUTH  PARTS  OF  IRON.  $1 

Test  the  thing  in  water  also :  here  the  result  is  more  sure  and 
more  easily  obtained.  Pass  through  a  round  cork  an  iron  wire 
two  or  three  fingers  long,  more  or  less,  so  that  it  may  just  float 
in  water:  the  moment  you  put  it  in  the  water  it  turns  round 
on  its  centre,  and  one  end  of  the  wire  travels  to  the  north,  the 
other  to  the  south :  the  cause  of  this,  you  will  find  later,  when 
we  treat  of  the  reasons  of  the  loadstone's  directions.  And  * 
it  is  well  to  know  and  to  hold  fast  in  memory,  that  as  a  strong 
loadstone  and  iron  magnetized  by  the  same,  point  not  always 
toward  the  true,  pole,  but  exactly  to  the  point  of  variation  ; 
likewise  will  a  weaker  loadstone  and  iron  that  directs  itself  by 
its  own  force,  and  not  by  force  derived  from  the  impress  of 
any  magnet ;  so,  too,  all  iron  ores,  and  all  substances  imbued 
with  any  ferric  matter  and  duly  prepared,  turn  to  the  same 
point  in  the  horizon — to  the  place  of  variation  of  the  locality 
concerned  (if  variation  exist  there),  and  there  they  remain  and 
rest. 


CHAPTER  XIII. 

SMELTED  IRON  HAS  IN  ITSELF  FIXED  NORTH  AND  SOUTH 
PARTS,  MAGNETIC  ACTIVITY,  VERTICITY,  AND  FIXED 
VERTICES   OR  POLES. 

Iron  takes  a  direction  toward  north  and  south,  but  not* 
with  the  same  point  directed  toward  either  pole  ;  for  one  end 
of  a  piece  of  iron  ore  or  of  an  iron  wire  steadily  and  constantly 
points  to  the  north  and  the  other  to  the  south,  whether  it  be 
suspended  in  air,  or  floating  in  water,  and  whether  the  speci- 
mens be  iron  bars  or  thin  wires.     Even  an  iron  rod  or  wire  ten, 


52  WILLIAM  GILBERT. 

twenty,  or  more  ells  in  length  will  point  with  one  extremity  to 
the  north,  with  the  other  to  the  south.  And  if  you  cut  off  a 
part,  if  the  farther  end  of  that  piece  is  boreal  (northern),  the 
farther  end  of  the  other  piece,  with  which  it  was  before  joined, 
will  be  austral  (southern).  And  so,  if  you  divide  the  rod  or 
wire  into  several  pieces,  you  shall  know  the  poles  even  before 
you  make  an  experiment  by  floating  the  pieces  in  water.  In 
all  these  fragments  a  boreal  end  attracts  an  austral,  and  repels 
a  boreal,  and  vice  versa,  according  to  magnetic  law.  But,  herein, 
manufactured  iron  so  differs  from  loadstone  and  iron  ore,  that 
in  a  ball  of  iron  of  whatever  size — e.g.,  bombs,  cannon-balls, 
culverin  balls,  falcon  balls — polarity  (verticity)  is  less  easily 
acquired  and  less  readily  manifested  than  in  the  loadstone 
itself,  in  ore,  and  in  a  round  loadstone  ;  but  in  iron  instruments 
of  any  length  the  force  is  at  once  seen :  the  cause  of  which,  as 
also  the  modes  of  acquiring  polarity  and  poles  without  a  load- 
stone, together  with  the  account  of  all  other  recondite  facts 
touching  verticity,  we  will  set  forth  when  we  come  to  treat  of 
the  movement  of  direction. 


CHAPTER  XIV. 

OF    OTHER   PROPERTIES    OF   THE    LOADSTONE    AND    OF    ITS 
MEDICINAL    VIRTUE. 

DiOSCORlDES  tells  that  loadstone  blended  in  water  is  ad- 
ministered in  a  dose  of  three  oboli'  to  expel  gross  humors. 
Galen   writes   that  it   has  virtues   like  those   of   bloodstone. 

'  Obolus,  the  sixth  part  of  a  drachm. 


OTHER  PROPERTIES  OF   THE  LOADSTONE.  53 

Others  say  that  loadstone  causes  mental  disturbance  and 
makes  people  melancholic,  and  often  is  fatal.  Gartias  ab 
Horto  does  not  think  it  injurious  or  unwholesome.  The  people 
of  East  India,  he  says,  declare  that  loadstone  taken  in  small 
quantity  preserves  youthfulness:  for  this  reason  the  elder  King 
Zeilam  (Zeilan)  is  said  to  have  ordered  made  of  loadstone  some 
pans  for  cooking  his  food  ivictus).  "  The  man  who  was  ordered 
to  do  this  thing  told  me,"  says  Gartias.*  Many  are  the  varie- 
ties of  loadstone,  produced  by  different  mixtures  of  earths, 
metals,  and  humors ;  therefore  are  they  totally  different  in 
their  virtues  and  effects,  according  to  the  neighborhoods  of 
places  and  the  nearness  of  adhering  bodies,  and  the  pits  them- 
selves— unclean  matrices,  as  it  were.  Hence  one  loadstone  is 
able  to  purge  the  bowels,  and  another  loadstone  to  stay  the 
purging ;  with  a  sort  of  fumes,  it  can  gravely  affect  the  mind  ; 
it  may  corrode  the  stomach  and  produce  in  it  serious  disease : 
for  such  disorders,  quacks  prescribe  gold  and  emerald,  prac- 
tising the  vilest  imposture  for  lucre's  sake.  Pure  loadstone 
also  may  be  harmless  ;  and  not  only  that,  but  many  correct  ex- 
cessive humors  of  the  bowels  and  putrescence  of  the  same,  and 
may  bring  about  a  better  temperature :  such  loadstones  are 
the  Oriental  ones  from  China,  the  more  compact  loadstones  of 


1  Garcia  d'Orta,  "Coloquios  dos  simples  ....  pello  doutor  Garcia 
Dorta"  (sic) — Goa  1563.  The  name  of  the  Portuguese  author  of  this  rare  work 
— who  was  physician  to  the  Spanish  Viceroy  (Brown's  "Vulgar  Errors,"  Book 
II,  page  81) — appears  as  Garcia  ab  Horto  in  the  abridged  Latin  translation 
made  by  Charles  de  I'Ecluse,  Antwerp  1567,  1574,  1579,  1593,  under  title 
"Aromatumet  Simplicium  .  .  .  ,"  and  it  is  rendered  in  French  Garcie  du 
Jardin,  by  Antoine  Colin  in  his  "  Histoire  des  Drogues,"  Lyon  1619,  whilst 
in  other  versions  it  is  given  as  Garcia  del  Huerto.  For  the  passage  above 
alluded  to  by  Gilbert,  see,  more  particularly,  the  last  (1593)  edition,  article  T>e 
Magneie,  Lib.  I,  Cap.  LVI,  pages  178,  179.  Hakewill  observes  ("  Apologie," 
1635,  Lib.  II,  page  165),  "Remarkable  indeed  that  is  which  Garziasab  Horto 
writes  concerning  the  load-stone  in  Simpl  Indice,  Lib.  I,  Cap.  XLVII." 


54  WILLIAM  GILBERT. 

Bengal :  these  kinds  of  loadstone  are  not  distasteful  nor  un- 
grateful to  the  senses.  Plutarch  and  Caius  Ptolemy,  and  all 
the  copyists  that  came  after  them,  believe  that  loadstone 
rubbed  with  garlic  does  not  attract  iron.  Hence  some  writers 
conjecture  that  garlic  is  of  service  against  the  harmful  action 
of  loadstone  :  in  this  way  does  many  an  untrue  and  vain  opinion 
in  philosophy  take  its  rise  in  fables  and  falsehoods.'  Not  a 
few  physicians  have  thought  that  loadstone  has  power  to  ex- 
tract an  iron  arrow-head  from  a  human  body :  but  a  loadstone 
attracts  when  it  is  whole,  not  when  reduced  to  powder,  de- 
formed, buried  in  a  plaster ;  for  it  does  not  with  its  matter  at- 
tract in  such  case,  but  serves  rather  to  heal  the  ruptured  tissues 
by  exsiccation,  so  causing  the  wound  to  close  and  dry  up, 
whereby  the  arrow-head  becomes  fixed  in  the  wound.  Thus 
do  pretenders  to  science  vainly  and  preposterously  seek  for 
remedies,  ignorant  of  the  true  causes  of  things.  Headaches, 
despite  the  opinion  of  many,  are  no  more  cured  by  application 
of  a  loadstone,  than  by  putting  on  the  head  an  iron  helmet  or 
a  steel  hat.  Administration  of  loadstone  to  dropsical  persons 
is  either  an  error  of  the  ancients  or  a  blundering  quotation  of 
their  transcribers,  albeit  a  loadstone  may  be  found  capable  of 
purging  the  bowels,  after  the  manner  of  sundry  metallic  sub- 
stances :  but  the  effect  would  be  due  to  some  vice  of  the  stone, 
not  to  its  magnetic  force.  Nicolaus  puts  into  his  "  divine 
plaster"  a  good  deal  of  loadstone,  as  do  the  Augsburg  doctors 
in  their  "  black  plaster"  for  fresh  wounds  and  stabs ;  because 
of  the  exsiccating  effect  of  the  loadstone  without  corrosion,  it 
becomes  an  efficacious  and  useful  remedy,  Paracelsus,  in  like 
manner  and  for  the  same  end,  makes  loadstone  an  ingredient 
of  his  plaster  for  stab-wounds. 

*  See  note,  Book  I,  Chap.  I,  of  present  work. 


THE  MEDICINAL  POWER   OF  THE  IRON.  55 


CHAPTER  XV. 

THE   MEDICINAL   POWER   OF  THE   IRON. 

It  will  not  be  alien  to  our  purpose  to  treat  briefly  of  the 
medicinal  power  of  iron  ;  for  it  is  beneficial  in  many  diseases 
of  the  human  system,  and  by  its  virtues,  both  natural  and 
acquired  through  fit  and  skilful  preparation,  it  brings  about  won- 
derful changes  in  the  human  body  ;  so  that  we  may  more  clearly 
describe  its  nature  through  its  medicinal  power  and  by  means 
of  a  few  well-known  experiments ;  to  the  end  that  even  those 
prentices  of  medicine  who  abuse  this  most  excellent  medicinal 
agent  may  learn  to  prescribe  it  more  judiciously,  for  the  curing 
of  patients,  not  as  is  too  often  the  case,  to  their  destruction. 
The  best  iron,  i.e.,  stomoma,  chalybs,  acies,  or  aciarium  (steel), 
is  reduced  by  filing  to  a  fine  powder  ;  this  powder  has  strongest 
vinegar  poured  on  it,  is  dried  in  the  sun,  again  treated  with 
vinegar,  and  once  more  dried.  Then  it  is  washed  in  spring 
water  or  other  water  at  hand,  and  dried.  It  is  again  pulverized 
and  pounded  fine  on  porphyry,  sifted  through  a  fine  sieve,  and 
kept  for  use.  It  is  given  chiefly  in  cases  of  lax  and  over- 
humid  liver,  and  in  cases  of  tumid  spleen  after  suitable  evacua- 
tions ;  hence  young  women  of  pale,  muddy,  blotchy  complexion 
are  by  it  restored  to  soundness  and  comeliness,  for  it  is  highly 
exsiccative  and  harmlessly  astringent.  But  some,  who  in  every 
internal  disorder  always  recognize  obstructions  of  liver  and 
spleen,  think  it  beneficial  in  such  cases,  as  removing  obstruc- 
tions ;  and  herein  they  accept  the  opinions  chiefly  of  certain 
Arabic  writers.     Hence  in  cases  of  dropsy,  schirrus  of  the 


$6  WILLIAM  GILBERT. 

liver,  of  chronic  jaundice,  and  hypochondriac  melancholia,  or 
complaints  of  the  oesophagus,  they  prescribe  it,  or  add  it  to 
electuaries,  often  to  the  sure  destruction  of  many  a  patient.' 
Fallopius  recommends  a  preparation  of  iron  of  his  own  for 
schirrus  of  the  spleen  ;  but  he  is  much  mistaken,  for  though 
loadstone  is  exceedingly  beneficial  where  the  spleen  is  lax  and 
tumid  on  account  of  humors,  so  far  is  it  from  curing  a  spleen 
thickened  to  a  schirrus,  that  it  makes  the  mischief  far  worse ; 
for  agents  that  are  greatly  siccative  and  that  absorb  humors, 
transform  viscera  that  have  been  thickened  by  schirrus,  into 
the  hardness  almost  of  a  stone.  Some  there  are  who  dry  it 
at  a  high  temperature  in  an  oven,  burning  it  till  its  color  is 
changed  to  red  :  it  is  then  called  "saffron  of  Mars,""  and  is  a 
very  powerful  exsiccant  and  quickly  penetrates  the  intestines. 
Further,  they  prescribe  violent  exercise  so  that  the  remedy 
may  enter  the  heated  intestines  and  reach  the  part  affected. 
Hence  it  is  reduced  to  a  very  fine  powder;  else  it  would  re- 
main in  the  oesophagus  and  in  the  chyle  and  would  not  pene- 
trate to  the  intestines.  Therefore  this  dry,  earthly  medicament 
is  proved  by  the  most  conclusive  tests  to  be,  after  due  evacua- 
tions, a  remedy  in  diseases  arising  from  humor  (when  the  intes- 
tines are  running  and  overflowing  with  morbid  fluids).  A 
preparation  of  steel  is  indicated  for  tumid  spleen ;  chalybeate 
waters  also  reduce  the  spleen,  albeit,  as  a  rule,  iron  is  of  frigid 
efificiency  and  a  constringent  rather  than  a  resolvent ;  but  it 
does  this  neither  by  heat  nor  by  cold,  but  by  its  own  dryness 

'  "  The  magnet  ....  gives  comfort  and  grace,  and  is  a  cure  for  many  com- 
plaints, it  is  of  great  value  in  disputes.  When  pulverized,  it  cures  many  burns. 
It  is  a  remedy  for  dropsy  "  (J.  Sermone di  F.  Sacchetti ,  §  i8).  Ac- 
cording to  Dias,  "the  magnet  reconciles  husbands  to  their  wives,"  and  Platea 
remarks  that  "it  is  principally  of  use  to  the  wounded,"  while  Avicenna  says 
it  "  is  a  remedy  against  spleen,  the  dropsy,  and  alopecian." 

'■*  See  Book  II,  Chap.  XXIII. 


THE  MEDICINAL   POWER   OF    THE  IRON.  5/ 

when  mixed  with  a  penetrant  fluid ;  in  this  way  it  dissipates 
humors,  thickens  the  villi;  strengthens  the  fibres  and  when 
they  are  lax  makes  them  contract ;  then  the  natural  warmth  in 
the  organs  thus  strengthened  becoming  stronger  does  the  rest ; 
but  should  the  liver  be  indurated  and  impaired  through  age  or 
chronic  obstruction,  or  should  the  spleen  be  dried  up  and 
thickened  into  a  schirrhus,  under  which  complaints  the  flesh 
parts  of  the  members  become  atrophied,  and  water  collects  all 
over  the  body  under  the  skin — in  such  cases  the  preparation 
of  steel  does  but  hasten  a  fatal  result  and  makes  the  mischief 
worse.  Some  recent  authorities  prescribe,  as  a  highly  com- 
mended and  celebrated  remedy  for  dried-up  liver,  an  electuary 
of  iron  slag  described  by  Razes  (Rhazes — Abu  Bekr  Arrasi)  in 
hoo\i  mvA!i\.  Ad Almansorem,  or  of  prepared  steel  filings:  bad 
and  pernicious  counsel.  But  now  if  they  never  will  learn  from 
our  philosophy,  at  least  daily  experience  and  the  decline  and 
death  of  their  patients  will  convince  them,  slow  and  sluggish 
as  they  are.  Whether  iron  be  warm  or  cold  is  a  question  over 
which  many  contend.  Manardus,  Curtius,  Fallopius,  and  others 
bring  many  arguments  for  both  sides  :  every  one  judges  accord- 
ing to  his  own  way  of  looking  at  it.  Some  will  have  it  cold, 
saying  that  iron  has  the  power  of  refrigeration,  since  Aristotle 
in  the  Meteorologica  declares  it  to  belong  to  the  class  of  bodies 
that  become  concreted  through  cold  by  emission  of  all  their 
warmth.  Galen,  too,  says  that  iron  gets  its  consistency  from 
cold  ;  further,  that  it  is  an  earthy  body  and  dense.  It  is  de- 
clared to  be  cold  also  because  it  is  astringent,  and  ^  because 
chalybeate  water  stills  thirst ;  they  mention  also  the  sensation 
of  coolness  produced  by  thermic  chalybeate  waters.  But  others 
hold  it  to  be  warm,  since  Hippocrates  says  that  chalybeate 
waters  issuing  from  places  where  iron  exists  are  warm.  Galen 
says  that  in  all  metals  there  is  much  substance  or  essence  of 


58  WILLIAM  GILBERT. 

fire.  Razes  will  have  it  that  iron  is  warm  and  dry  in  the  third 
degree.  The  Arabs  hold  that  iron  opens  the  spleen  and  the 
liver :  hence  it  is  warm.  Montagnana  recommends  it  for  frigid 
complaints  of  uterus  and  oesophagus.  And  thus  do  sciolists 
wrangle  with  one  another,  and  confuse  the  minds  of  learners 
with  their  questionable  cogitations,  and  debate  over  the  ques- 
tion of  goat's  wool,  philosophizing  about  properties  illogically 
inferred  and  accepted :  but  these  things  will  appear  more 
plainly  when  we  come  to  treat  of  causes,  the  murky  cloud  being 
dispersed  that  has  so  long  involved  all  philosophy.  Iron  filings, 
iron  scales,  iron  dross,  do  not,  says  Avicenna,  lack  harmful 
quality  (perhaps  when  they  are  not  properly  prepared,  or  are 
taken  in  too  large  doses),  hence  they  produce  violent  intes- 
tinal pains,  roughness  in  the  mouth  and  on  the  tongue, 
marasmus,  and  drying  up  of  the  members.  But  mistakenly 
and  old  womanishly  does  Avicenna  declare  that  the  true  anti- 
dote of  this  ferric  poison  is  a  drachm  of  loadstone  taken  in  a 
draught  of  the  juice  of  dog's  mercury  or  of  beet-root ;  for  load- 
stone too  is  of  a  twofold  nature,  and  often  is  injurious  and 
fatal  in  its  effects ;  neither  does  it  withstand  iron,  for  it  attracts 
it ;  nor  is  it  able  to  attract  when  drunk  as  a  powder  in  liquid ; 
rather  does  it  cause  the  self-same  mischiefs. 


IDENTITY  OF  LOADSTONE  AND  IRON  ORE.  59 


CHAPTER  XVI. 

THAT  LOADSTONE  AND  IRON  ORE  ARE  THE  SAME,  AND  THAT 
IRON  IS  OBTAINED  FROM  BOTH,  LIKE  OTHER  METALS  FROM 
THEIR  ORES  ;  AND  THAT  ALL  MAGNETIC  PROPERTIES  EX- 
IST, THOUGH  WEAKER,  BOTH  IN  SMELTED  IRON  AND  IN 
IRON  ORE. 

So  far  we  have  been  telling  of  the  nature  and  properties  of 
loadstone,  as  also  of  the  properties  and  nature  of  iron  ;  it  now 
remains  that  we  point  out  their  mutual  affinities — their  consan- 
guinity, so  to  speak — and  that  we  show  the  two  substances  to 
be  very  nearly  allied.  In  the  uppermost  part  of  the  terrestrial 
globe  or  its  superficies  of  detritus — its  rind  as  it  were — these 
two  bodies  come  into  being  and  are  generated  in  the  same 
matrix,  in  one  bed,  like  twins.  Strong  loadstones  are  mined 
from  separate  deposits,  and  weaker  loadstones  also  have 
their  own  beds.  Both  occur  in  iron  mines.  Iron  ore  occurs 
usually  by  itself,  unaccompanied  by  strong  loadstone  (for  the 
more  perfect  loadstones  occur  more  rarely).  A  strong  load- 
stone looks  like  iron  :  from  it  is  often  made  the  best  iron,  which 
the  Greeks  call  stomoma,  the  Latins  acies,  and  the  Barbarians, 
not  inappropriately,  aciare  or  aciarium.  This  stone  attracts  and 
repels  other  loadstones,  and  governs  their  directions ;  points  to 
the  earth's  poles,  attracts  molten  iron,  and  does  many  other 
wonderful  things,  some  of  which  we  have  already  mentioned, 
but  many  more  remain  yet  to  be  pointed  out.  A  weak  load- 
stone will  do  the  same,  but  less  forcefully :  and  iron  ore,  and 
also   smelted   iron  (if  they  be   prepared),  show  their  virtues 


6o  WILLIAM  GILBERT. 

*■  in  all  magnetic  experiments,  no  less  than  do  weak  magnets ; 
and  the  inert  iron  ore,  endowed  with  no  magnetic  powers, 
that  is  taken  out  of  the  mine,  becomes  awake  when  treated 
in  the  furnace  and  fittingly  prepared,  and  then  is  a  loadstone 

*  in  power  and  properties.  Sometimes  ironstone  or  iron 
ore  exerts  attractive  action  the  moment  it  comes  from  the 
mine,  and  without  being  prepared  in  any  way ;  native  iron, 
also,  or  ore  of  iron  color,  attracts  iron  and  makes  it  point 
to  the  poles.  Thus  the  form,  appearance,  and  essence  are  one. 
For  to  me  there  seems  to  be  greater  difference  and  unlikeness 
between  a  very  strong  loadstone  and  a  weak  one  that  is  hardly 
able  to  attract  a  single  particle  of  iron  filings  ;  between  a  hard, 
firm,  and  metallic  loadstone  and  one  that  is  soft,  friable,  clayey, 
with  so  great  a  difference  between  them  in  color,  substance, 
qualities  and  weight;  than  between  the  best  ore,  rich  in  iron, 
or  iron  that  from  the  first  is  metallic,  on  the  one  hand,  and  the 
best  loadstone  on  the  other.  Nay,  the  two  are  usually  not  to 
be  distinguished  by  any  signs,  nor  can  miners  tell  one  from  the 
other,  for  they  agree  in  all  respects.  Further,  we  see  both 
the  finest  magnet  and  iron  ore  visited  as  it  were  by  the  same 
ills  and  diseases,  aging  in  the  same  way  and  with  the  same  in- 
dications, preserved  by  the  same  remedies  and  protective  meas- 
ures, and  so  retaining  their  properties :  so,  too,  the  one  adds 
to  the  other's  power  and  intensifies  and  increases  it,  when  the 
two  are  artificially  connected.  For  they  are  both  impaired  by 
the  action  of  acrid  liquids  as  though  by  poisons ;  the  aqua 
fortis  of  the  chemists  does  equal  injury  to  both;  exposed  for  a 
long  time  to  the  action  of  the  atmosphere  they  both,  in  equal  de- 
gree, age  as  it  were  and  decline  ;  each  is  saved  from  impairment 
by  being  kept  in  the  debris  and  scrapings  of  the  other,  and  a  suit- 
able piece  of  steel  or  iron  being  applied  to  its  pole,  the  mag- 
netic power  is  intensified  by  the  steadfast  union.     A  loadstone 


IDENTITY  OF  LOADSTONE  AND  IRON  ORE.  6l 

is  kept  in  iron  filings  not  as  though  it  fed  on  iron,  or  as  though 
it  were  a  hving  thing  needing  victual,  as  Cardan  philosophizes  ; 
neither  because  thus  it  is  protected  from  the  injurious  action  of 
the  atmosphere  (wherefore  both  the  loadstone  and  iron  are 
kept  in  bran  by  Scaliger;  though  Scaliger  is  mistaken  here,  for 
they  are  not  best  preserved  so,  and  loadstone  and  iron  in  some 
of  their  forms  last  a  long  time)  ;  but  because  each  is  kept  unim- 
paired in  filings  of  the  other  and  their  extremities  do  not  be- 
come weak,  but  are  cherished  and  preserved.  For  as  in  their 
native  sites  and  mines,  similar  bodies  surrounded  by  other 
bodies  of  the  same  kind,  e.g.,  the  minor  interior  parts  of  some 
great  mass,  endure  for  ages  whole  and  undecayed  ;  so  load- 
stone, and  iron  ore,  when  buried  in  a  like  material,  do  not  part 
with  their  native  humor,  and  do  not  become  weak,  but  retain 
their  original  properties.  A  loadstone  packed  in  iron  filings, 
as  also  iron  ore  in  scrapings  of  loadstone,  and  manufactured 
iron  in  the  same  or  in  iron  filings,  lasts  longer.  Thus  these 
two  associated  bodies  possess  the  true,  strict  form  of  one  species, 
though,  because  of  their  outwardly  different  aspect  and  the  in- 
equality of  the  self-same  innate  potency,  they  have  hitherto 
been  by  all  held  to  be  different,  and  by  sciolists  to  be  specifi- 
cally different,  for  sciolists  have  not  understood  that  in  both 
substances  reside  exactly  the  same  potencies,  differing  however 
in  strength.  They  are  in  fact  true  parts  and  intimate  parts  of 
the  globe,  retaining  nature's  primal  powers  of  mutual  attrac- 
tion, of  mobility,  and  of  ordering  themselves  according  to  the 
position  of  the  globe  itself :  these  powers  they  impart  to  eacli 
other,  enhancing  each  other's  powers,  confirming  them,  taking 
them  from  each  other,  and  holding  them.  The  stronger  invig- 
orates the  weaker,  not  as  if  it  imparted  of  its  own  substance  or 
parted  with  aught  of  its  own  strength,  neither  by  injecting  into 
that  other  any  physical  substance  ;  but  the  dormant  power  of 


62  WILLIAM  GILBERT. 

one  is  awakened  by  the  other's  without  expenditure.  For  if 
with  one  loadstone  you  magnetize  one  thousand  compass 
needles  for  mariners'  use  that  loadstone  not  less  powerfully 
attracts  iron  than  it  did  before  ;  with  one  stone  weighing  a 
pound  any  one  can  suspend  in  air  looo  pounds  of  iron.  For 
if  one  were  to  drive  into  a  wall  a  number  of  iron  nails  weighing 
all  together  lOOO  pounds,  and  were  to  apply  to  them  an  equal 
number  of  other  nails  properly  magnetized  by  contact  with  a 
loadstone,  the  nails  would  plainly  hang  suspended  in  air  through 
the  power  of  one  single  stone.  Hence  this  is  not  the  action, 
work,  or  outlay  of  the  loadstone  solely,  for  the  iron,  which  is 
something  extracted  from  loadstone,  a  transformation  of  load- 
stone into  metal,  and  which  gains  force  from  the  loadstone  and 
(whatever  ore  it  may  have  been  derived  from)  by  its  proximity 
strengthens  the  loadstone's  magnetic  power,  at  the  same  time 
enhances  its  own  native  force  by  the  proximity  of  the  load- 
stone and  by  contact  therewith,  even  though  solid  bodies  inter- 
vene between  them.  Iron  touched  by  loadstone  renovates 
other  iron  by  contact  and  gives  it  magnetic  direction  ;  and 
that  does  the  same  for  a  third  piece  of  iron.  But  if  you  rub 
with  loadstone  any  other  metal,  or  wood,  or  bone,  or  glass,  as 
they  will  not  move  toward  a  fixed  and  determinate  quarter  of 
the  heavens,  nor  will  be  attracted  by  a  magnetized  body ;  so 
they  cannot  impart  by  attrition  or  by  infection  any  magnetic 
property  either  to  other  bodies  or  to  iron  itself.  Loadstone 
differs  from  iron  ore,  as  also  from  some  weak  loadstones,  in  that 
when  reduced  in  the  furnace  to  a  ferric  and  metallic  molten 
mass,  it  does  not  always  assume  readily  the  fluid  condition  and 
become  changed  to  metal,  but  sometimes  is  burnt  into  ash  in 
the  large  furnaces ;  this,  either  because  of  a  certain  admixture 
of  sulphurous  matter,  or  because  of  its  own  excellence  and 
more  simple  nature ;    or  because  of  the  resemblance  it  bears 


IDENTITY  OF  LOADSTONE  AND  IRON  ORE.  63 

to  nature,  and  the  form  it  has  in  common  with  that  mother 
of  all ;    for  earths,  ferruginous  stones,  and  loadstones  rich  in 
metal,  are  much  loaded  and  disfigured   with  drossy  metallic 
humors  and  with  foreign  earthy  admixtures  in  their  substance, 
like  most  weak  magnets  from  the  mines  ;  hence  they  are  farther 
removed  from  the  common  mother  and  are  degenerate,  and  in 
the  furnace  they  are  more  easily  melted  and  give  a  softer  sort 
of  iron  and  no  good  steel.     Most  loadstones,  if  they  be  not  un- 
duly burnt,  yield  in  the  furnace  the  best  of  iron.     But  in  all 
these  prime  quahties  iron  ore  agrees  with  loadstone,  for  both, 
being  more  akin  to  the  earth  and  more  nearly  associated  to  it 
than  any  other  bodies  around  us,  possess  within  themselves  the 
magnetic,  genuine,  homogenic  and  true  substance  of  the  terres- 
trial globe,  less  tainted  and  impaired  by  foreign  impurities,  and 
less  mixed  with  the  efflorescences  on  the  earth's  surface  and 
the  debris  of  generations  of  organisms.     And  on  this  ground 
does  Aristotle  seem,  in  book  fourth  of  his  Meteora,  to  distinguish 
iron  from  all  other  metals.     Gold,  says  he,  silver,  copper,  tin, 
lead,  pertain  to  water ;  but  iron  is  earthy.     Galen,  in  the  fourth 
book  De  Facultatibus  Simplicium  Medicament  or  um,  says  that 
iron  is  an  earthy  and  dense  body.     So,  according  to  our  rea- 
soning, loadstone  is  chiefly  earthy  ;  next  after  it  comes  iron  ore 
or  weak  loadstone ;  and  thus  loadstone  is  by  origin  and  nature 
ferruginous,  and  iron  magnetic,  and  the  two  are  one  in  species. 
Iron  ore  in  the  furnace  yields  iron ;   loadstone  in  the  furnace 
yields  iron  also,  but  of  far  finer  quality,  which  is  called  steel ; 
and  the  better  sort  of  iron  ore  is  weak  loadstone,  just  as  the 
best  loadstone  is  the  most  excellent  iron  ore  in  which  we  will 
show  that   grand  and  noble   primary   properties  inhere.     It 
is  only  in  weaker  loadstone,  or  iron  ore,  that  these  properties 
are  obscure,  or  faint,  or  scarcely  perceptible  to  the  senses. 


64  WILLIAM   GILBERT. 


CHAPTER  XVII. 

THAT  THE  TERRESTRIAL  GLOBE  IS  MAGNETIC  AND  IS  A  LOAD- 
STONE ;  AND  JUST  AS  IN  OUR  HANDS  THE  LOADSTONE 
POSSESSES  ALL  THE  PRIMARY  POWERS  (FORCES)  OF  THE 
EARTH,  SO  THE  EARTH  BY  REASON  OF  THE  SAME  POTEN- 
CIES LIES  EVER  IN  THE  SAME  DIRECTION  IN  THE  UNI- 
VERSE. 

Before  we  expound  the  causes  of  the  magnetic  movements 
and  bring  forward  our  demonstrations  and  experiments  touch- 
ing matters  that  for  so  many  ages  have  lain  hid — the  real 
foundations  of  terrestrial  philosophy — we  must  formulate  our 
new  and  till  now  unheard-of  view  of  the  earth,  and  submit  it 
to  the  judgment  of  scholars.  When  it  shall  have  been  sup- 
ported with  a  few  arguments  of  prima  facie  cogency,  and  these 
shall  have  been  confirmed  by  subsequent  experiments  and 
demonstrations,  it  will  stand  as  firm  as  aught  that  ever  was  pro- 
posed in  philosophy,  backed  by  ingenious  argumentation,  or  but- 
tressed by  mathematical  demonstrations.  The  terrestrial  mass 
which  together  with  the  world  of  waters  produces  the  spherical 
figure  and  our  globe,  inasmuch  as  it  consists  of  firm  durable 
matter,  is  not  easily  altered,  does  not  wander  nor  fluctuate  with 
indeterminate  movements  like  the  seas  and  the  flowing  streams  ; 
but  in  certain  hollows,  within  certain  bounds,  and  in  many 
veins  and  arteries,  as  it  were,  holds  the  entire  volume  of  liquid 
matter,  nor  suffers  it  to  spread  abroad  and  be  dissipated.  But 
the  solid  mass  of  the  earth  has  the  greater  volume  and  holds 
preeminence  in  the  constitution  of  our  globe.     Yet  the  water  is 


THE    TERRESTRIAL    GLOBE  A   LOADSTONE.  65 

associated  with  it,  though  only  as  something  supplementary 
and  as  a  flux  emanating  from  it ;  and  from  the  beginning  it  is 
intimately  mixed  with  the  smallest  particles  of  earth  and  is 
innate  in  its  substance.  The  earth  growing  hot  emits  it  as 
vapor,  which  is  of  the  greatest  service  to  the  generation  of 
things.  But  the  strong  foundation  of  the  globe,  its  great  mass, 
is  that  terrene  body,  far  surpassing  in  quantity  the  whole 
aggregate  of  fluids  and  waters  whether  in  combination  with 
earth  or  free  (whatever  vulgar  philosophers  may  dream  about 
the  magnitudes  and  proportions  of  their  elements) ;  and  this 
mass  makes  up  most  of  the  globe,  constituting  nearly  its  whole 
interior  framework,  and  of  itself  taking  on  the  spherical  form. 
For  the  seas  do  but  fill  certain  not  very  deep  hollows,  having 
very  rarely  a  depth  of  a  mile,  and  often  not  exceeding  100  or 
50  fathoms.  This  appears  from  the  observations  of  navigators 
who  have  with  line  and  sinker  explored  their  bottoms.  In  view 
of  the  earth's  dimension,  such  depressions  cannot  much  impair 
the  spheroidal  shape  of  the  globe.  Still  the  portion  of  the 
earth  that  ever  comes  into  view  for  man  or  that  is  brought  to 
the  surface  seems  small  indeed,  for  we  cannot  penetrate  deep 
into  its  bowels,  beyond  the  debris  of  its  outermost  efflorescence, 
hindered  either  by  the  waters  that  flow  as  through  veins  into 
great  mines  ;  or  by  the  lack  of  wholesome  air  necessary  to  sup- 
port the  life  of  the  miners ;  or  by  the  enormous  cost  of  exe- 
cuting such  vast  undertakings,  and  the  many  difficulties  attend- 
ing the  work.  Thus  we  cannot  reach  the  inner  parts  of  the 
globe,  and  if  one  goes  down,  as  in  a  few  mines,  400  fathoms,  or 
(a  very  rare  thing)  500  fathoms,  it  is  something  to  make  every 
one  wonder.  But  how  small,  how  almost  null,  is  the  proportion 
of  500  fathoms  to  the  earth's  diameter,  6,872  miles,  can  be  easily 
understood.  So  we  do  only  see  portions  of  the  earth's  circum- 
ference, of  its  prominences  ;   and  everywhere  these  are  either 


66 


WILLIAM  GILBERT. 


loamy,  or  argillaceous,  or  sandy  ;  or  consist  of  organic  soils  or 
marls ;  or  it  is  all  stones  and  gravel ;  or  we  find  rock-salt,  or 
ores,  or  sundry  other  metallic  substances.  In  the  depths  of 
the  ocean  and  other  waters  are  found  by  mariners,  when  they 
take  soundings,  ledges  and  great  reefs,  or  bowlders,  or  sands, 
or  ooze.  The  Aristotelian  element,  earth,  nowhere  is  seen, 
and  the  Peripateties  are  misled  by  their  vain  dreams  about 
elements.  But  the  great  bulk  of  the  globe  beneath  the  sur- 
face and  its  inmost  parts  do  not  consist  of  such  matters ;  for 
these  things  had  not  been  were  it  not  that  the  surface  was  in 
contact  with  and  exposed  to  the  atmosphere,  the  waters,  and 
the  radiations  and  influences  of  the  heavenly  bodies ;  for  by 
the  action  of  these  are  they  generated  and  made  to  assume 
many  different  forms  of  things,  and  to  change  perpetually. 
Still  do  they  imitate  the  inner  parts  and  resemble  their  source, 
because  their  matter  is  of  the  earth,  albeit  they  have  lost  the 
prime  qualities  and  the  true  nature  of  terrene  matter ;  and  they 
bear  toward  the  earth's  centre  and  cohere  to  the  globe  and  can- 
not be  parted  from  it  save  by  force.  Yet  the  loadstone  and  all 
magnetic  bodies — not  only  the  stone  but  all  magnetic,  homo- 
genic  matter — seem  to  contain  within  themselves  the  potency 
of  the  earth's  core  and  of  its  inmost  viscera,  and  to  have  and 
comprise  whatever  in  the  earth's  substance  is  privy  and  inward  : 
the  loadstone  possesses  the  actions  peculiar  to  the  globe,  of  at- 
traction, polarity,  revolution,  of  taking  position  in  the  universe 
according  to  the  law  of  the  whole ;  it  contains  the  supreme 
excellencies  of  the  globe  and  orders  them  :  all  this  is  token  and 
proof  of  a  certain  eminent  combination  and  of  a  most  accord- 
ant nature.  For,  if  among  bodies  one  sees  aught  that  moves 
and  breathes  and  has  senses  and  is  governed  and  impelled  by 
reason,  will  he  not,  knowing  and  seeing  this,  say  that  here  is  a 
man  or  something  more  like  man  than  a  stone  or  a  stalk  ?    The 


THE    TERRESTRIAL   GLOBE  A    LOADSTONE.  6/ 

loadstone  far  surpasses  all  other  bodies  around  us  in  the 
virtues  and  properties  that  pertain  to  the  common  mother  of 
all ;  but  those  properties  have  been  very  little  understood  and 
noted  by  philosophers.  Toward  it,  as  we  see  in  the  case  of  the 
earth,  magnetic  bodies  tend  from  all  sides,  and  adhere  to  it ; 
it  has  poles — not  mathematical  points,  but  natural  points  of 
force  that  through  the  co-operation  of  all  its  parts  excel  in 
prime  efficiency;  such  poles  exist  also  in  the  same  way  in  the 
globe,  and  our  forefathers  always  sought  them  in  the  heavens. 
Like  the  earth,  it  has  an  equator,  a  natural  line  of  demarkation 
between  the  two  poles ;  for  of  all  the  lines  drawn  by  mathe- 
maticians on  the  terrestrial  globe,  the  equator  (as  later  will 
appear)  is  a  natural  boundary,  and  not  merely  a  mathematical 
circle.  Like  the  earth,  the  loadstone  has  the  power  of  direction 
and  of  standing  still  at  north  and  south ;  it  has  also  a  circular 
motion  to  the  earth's  position,  whereby  it  adjusts  itself  to  the 
earth's  law.  It  follows  the  elevations  and  depressions  of  the 
earth's  poles,  and  conforms  precisely  to  them  :  according  to  the 
position  of  the  earth  and  of  the  locaHty,  it  naturally  and  of 
itself  elevates  its  poles  above  the  horizon,  or  depresses  them. 
The  loadstone  derives  properties  from  the  earth  ex  tempore, 
and  acquires  verticity ;  and  iron  is  affected  by  the  verticity  of 
the  globe  as  it  is  affected  by  a  loadstone.  Magnetic  bodies 
are  governed  and  regulated  by  the  earth,  and  they  are  subject 
to  the  earth  in  all  their  movements.  All  the  movements  of  the 
loadstone  are  in  accord  with  the  geometry  and  form  of  the 
earth  and  are  strictly  controlled  thereby,  as  will  later  be  proved 
by  conclusive  experiments  and  diagrams  ;  and  the  greater  part 
of  the  visible  earth  is  also  magnetic,  and  has  magnetic  move- 
ments, though  it  is  defaced  by  all  sorts  of  waste  matter  and 
by  no  end  of  transformations.     Why,  then,  do  we  not  recog- 


6S  WILLIAM  GILBERT. 

nize  this  primary  and  homogeneous  earth-substance,  likest  of 
all  substances  to  the  inmost  nature,  to  the  very  marrow,  of  the 
earth  itself,  and  nearest  to  it  ?  For  not  any  of  the  other  mixed 
earths — those  suitable  for  agriculture, — not  any  of  the  metal- 
liferous veins,  no  stones,  no  sands,  no  other  fragments  of  the 
globe  that  come  under  our  notice,  possess  such  stable,  such 
distinctive  virtues.  Yet  we  do  not  hold  the  v/hole  interior  of 
this  our  globe  to  be  of  rock  or  of  iron,  albeit  the  learned 
Franciscus  Maurolycus  ^  deems  the  earth  in  its  interior  to  con- 
sist throughout  of  rigid  rock.  For  not  every  loadstone  that 
we  find  is  a  stone,  being  sometimes  like  a  clod  of  earth,  or  like 
clay,  or  like  iron  ;  consisting  of  various  materials  compacted 
into  hardness,  or  soft,  or  by  heat  reduced  to  the  metallic  state  ; 
and  in  the  earth's  surface  formations,  according  to  circum- 
stances of  place,  of  the  bodies  around  it,  and  of  its  matrix  in 
the  mine,  a  magnetic  substance  is  distinguished  by  divers 
qualities  and  by  adventitious  accretions,  as  we  see  in  marl, 
in  some  stones,  and  in  iron  ores.  But  the  true  earth-matter 
we  hold  to  be  a  solid  body  homogeneous  with  the  globe, 
firmly  coherent,  endowed  with  a  primordial  and  (as  in  the 
other  globes  of  the  universe)  an  energic  form.  By  being  so 
fashioned,  the  earth  has  a  fixed  verticity,  and  necessarily  re- 
volves with  an  innate  whirling  motion  :  this  motion  the  load- 
stone alone  of  all  the  bodies  around  us  possesses  genuine  and 


'  Francis  Maurolico — Maurolycus,  MaruUo  (1494-1575) — was  abbot  of 
Messina,  where  he  publicly  taught  mathematics,  and  was  quite  a  voluminous 
writer  upon  different  scientific  subjects,  his  works  including  very  able  treatises, 
more  particularly  on  the  sphere,  on  astronomical  instruments,  etc.  A  full 
account  of  his  life  and  writings  was  issued  at  Messina  (Messanae)  in  1613,  the 
date  and  place  likewise  of  his  very  interesting  magnetical  book  entitled  "  Prob- 
lemata  mechanica,  cum  appendice  et  ad  magnetem,  et  ad  pixidem  nauticam 
pertinentia." 


THE    TERRESTRIAL   GLOBE  A   LOADSTONE.  69 

true,  less  spoilt  by  outside  interferences,  less  marred  than  in 
other  bodies, — as  though  the  motion  were  an  homogeneous 
part  taken  from  the  very  essence  of  our  globe.  This  pure 
native  iron  is  produced  when  homogenic  portions  of  the 
earth's  substance  coalesce  to  form  a  metallic  vein  ;  loadstone 
is  produced  when  they  are  transformed  into  metallic  stone  or 
a  vein  of  the  finest  iron  or  steel ;  so,  too,  rather  imperfect 
homogenic  material  collects  to  form  other  iron  ores — just  as 
many  parts  of  the  earth,  even  parts  that  rise  above  the  general 
circumference,  are  of  homogenic  matter,  only  still  more  de- 
based. Native  iron  is  iron  fused  and  reduced  from  homogenic 
matters,  and  coheres  to  earth  more  tenaciously  than  the  ores 
themselves.  Such,  then,  we  consider  the  earth  to  be  in  its  in- 
terior parts ;  it  possesses  a  magnetic  homogenic  nature.  On 
this  more  perfect  material  (foundation)  the  whole  world  of 
things  terrestrial,  which,  when  we  search  diligently,  manifests 
itself  to  us  everywhere,  in  all  the  magnetic  metals  and  iron  ores 
and  marls,  and  multitudinous  earths  and  stones  ;  but  Aristotle's 
"  simple  element,"  and  that  most  vain  terrestrial  phantasm  of 
the  Peripatetics, — formless,  inert,  cold,  dry,  simple  matter,  the 
substratum  of  all  things,  having  no  activity, — never  appeared 
to  any  one  even  in  dreams,  and  if  it  did  appear  would  be  of 
no  effect  in  nature.  Our  philosophers  dreamt  only  of  an  inert 
and  simple  matter.  Cardan  thinks  the  loadstone  is  not  a  stone 
of  any  species,  but  that  it  is,  as  it  were,  a  perfect  portion  of  a 
certain  kind  of  earth  that  is  absolute,  whereof  a  proof  is  its 
abundance,  for  there  is  no  place  where  it  is  not  found.  He 
says  that  this  kind  of  conceptive,  generative  earth,  possessed 
of  an  aflfinity  like  that  of  the  marriage  tie,  is  perfected  when 
it  has  been  placed  in  contact  with,  or  received  the  fecundating 
influence  of,  the  masculine  or  Herculean  stone,  it  having  been, 


70  WILLIAM  GILBERT. 

moreover,  shown  in  a  previous  proposition  {Libro  de  Proper- 
tionibus)  that  the  loadstone  is  true  earth.  ' 

A  strong  loadstone  shows  itself  to  be  of  the  inmost  earth, 
and  in  innumerable  experiments  proves  its  claim  to  the  honor 
of  possessing  the  primal  form  of  things  terrestrial,  in  virtue  of 
which  the  earth  itself  remains  in  its  position  and  is  directed  in 
its  movements.  So  a  weak  loadstone,  and  all  iron  ore,  all 
marls  and  argillaceous  and  other  earths  (some  more,  some  less, 
according  to  the  difference  of  their  humors  and  the  varying 
degrees  in  which  they  have  been  spoilt  by  decay),  retain,  de- 
formed, in  a  state  of  degeneration  from  the  primordial  form, 
magnetic  properties,  powers,  that  are  conspicuous  and  in  the 
true  sense  telluric.  For  not  only  does  metallic  iron  turn  to  the 
poles,  not  only  is  one  loadstone  attracted  by  another  and  made 
to  revolve  magnetically,  but  so  do  (if  prepared)  all  iron  ores 
and  even  other  stones,  as  slates  from  the  Rhineland,  the  black 
slates  {ardoises,  as  the  French  call  them)  from  Anjou,  which 
are  used  for  shingles,  and  other  sorts  of  fissile  stone  of  different 
colors ;  also  clays,  gravel,  and  several  sorts  of  rock  ;  and,  in 
short,  all  of  the  harder  earths  found  everywhere,  provided 
only  they  be  not  fouled  by  oozy  and  dank  defilements  like 
mud,  mire,  heaps  of  putrid  matter,  or  by  the  decaying  remains 
of  a  mixture  of  organic  matters,  so  that  a  greasy  slime  oozes 
from  them,  as  from  marl, — they  are  all  attracted  by  the  load- 
stone, after  being  prepared  simply  by  the  action  of  fire  and 
freed  from  their  excrementitious  humor ;  and  as  by  the  load- 
stone, so,  too,  are  they  magnetically  attracted  and  made  to 
point  to  the  poles  by  the  earth  itself,  therein  differing  from  all 

^  Consult  Cardan's  Works,  Lugduni  (Lyons),  1663  ed.,  Vol.  II,  De  Ex- 
emplo. . . .,  pages  539,  546,  Vol.  HI,  Lib.  V,  Cap.  XVII-XIX,  Vol.  X,  Cap.  VI, 
page  12. 


THE    TERRESTRIAL   GLOBE  A   LOADSTONE. 


71 


other  bodies ;  and  by  this  innate  force  they  are  made  to  con- 
form to  the  ordering  and  planning  of  the  universe  and  the 
earth,  as  later  will  appear.  Thus  every  separate  fragment  of 
the  earth  exhibits  in  indubitable  experiments  the  whole  im- 
petus of  magnetic  matter  ;  in  its  various  movements  it  follows 
the  terrestrial  globe  and  the  common  principle  of  motion. 


BOOK  SECOND. 


CHAPTER  L 

OF  MAGNETIC   MOVEMENTS. 

Of  opinions  touching  the  loadstone  and  its  varieties ;  of  its 
poles  and  its  recognized  faculties  {facultatibus) ;  of  iron  and  its 
properties ;  of  the  magnetic  substance  common  to  loadstone 
and  iron  and  the  earth  itself, — we  have  treated  briefly  in  the 
foregoing  book.  Now  remain  the  magnetic  movements  and 
their  broader  philosophy  as  developed  by  experiments  and 
demonstrations.  These  movements  are  impulsions  of  homo- 
geneous parts  toward  one  another  or  toward  the  primary  con- 
formation of  the  whole  earth.  Aristotle  admits  only  two 
simple  movements  of  his  elements — from  the  centre  and 
toward  the  centre ;  light  objects  upward,  heavy  objects  down- 
ward :  so  that  in  the  earth  there  is  but  one  motion  of  all  its 
parts  toward  the  centre  of  the  world, — a  wild  headlong  falling. 
We,  however,  will  elsewhere  consider  what  this  '  light '  may 

be,  and  will  show  how  erroneously  it  is  inferred  by  the  Peri- 

72 


OF  MAGNETIC  MOVEMENTS.  73 

patetics  from  the  simple  motion  of  the  elements ;  we  shall 
also  inquire  what  'heavy'  means.'  But  now  we  have  to  in- 
quire into  the  causes  of  the  other  movements  depending  on 
its  true  form  :  these  we  see  clearly  in  all  magnetic  bodies ;  these 
also  we  find  existing  in  the  earth  and  all  its  homogenic  parts ; 
further,  we  find  that  they  are  in  accord  with  the  earth,  and  are 
bound  up  in  its  forces.  Now  five  movements  or  differences  of 
movement  are  perceived  by  us :  CoiTlON  ^  (commonly  called 
attraction),  an  impulsion  to  magnetic  union ;  DIRECTION ' 
toward  the  earth's  poles,  and  verticity  of  the  earth  toward 
determinate  points  in  the  universe,  and  the  standstill  there ; 
VARIATION,"  deflection  from  the  meridian, — this  we  call  a  per- 
verted motion  ;  DECLINATION  '  (inclination  or  dip),  a  descent 
of  the  magnetic  pole  beneath  the  horizon  ;  and  circular  move- 
ment, or  REVOLUTION.^  Of  each  of  these  we  will  treat  sepa- 
rately, and  will  show  how  they  all  proceed  from  a  congregant 
nature,  or  from  verticity  or  from  volubility.  Jofrancus  Offusius 
distinguishes  several  magnetic  movements,  the  first  to  the 
centre,  the  second  to  the  pole,  traversing  jy  degrees,  the  third 
to  iron,  the  fourth  to  a  loadstone.  The  first  is  not  always  to 
the  centre,  for  only  at  the  poles  is  it  in  a  right  line  to  the 
centre,  if  the  motion  is  magnetic,  otherwise  it  is  only  the 
movement  of  matter  toward  its  mass  and  toward  the  earth. 
The  second,  of  J'j  degrees  to  the  pole,  is  no  movement,  but  a 
direction  or  a  variation  to  the  earth's  pole.  The  third  and 
the  fourth  are  magnetic,  and  are  but  one  movement.  Thus 
this  author  recognizes  no  true  magnetic  movement  but  coition 


'  See   Plato's    Timceus  (tr.   of  Mr.    Henry    Davis),    London    1849,  Vol.  II, 
pages  372-374. 

*  See  Book  II,  Chap.  II,  et  seq.  3  See  Book  III. 

^  See  Book  IV.  «  See  Book  V. 

«  See  Book  VI,  Chap.  Ill,  et  seq. 


74  WILLIAM  GILBERT. 

toward  iron  or  loadstone,  commonly  known  as  attraction. 
There  is  another  movement  in  the  earth  as  a  whole,  which 
does  not  take  place  toward  the  terrella  or  the  parts,  i.e.^  the 
movement  of  coacervation  and  that  movement  of  matter 
called  by  philosophers  a  "  right  movement:"  of  that  elsewhere. 


CHAPTER   II. 

OF  MAGNETIC  COITION  ;  AND,  FIRST,  OF  THE  ATTRACTION  EX- 
ERTED BY  AMBER,  OR  MORE  PROPERLY  THE  ATTACHMENT 
OF  BODIES   TO   AMBER. 

Great  has  ever  been  the  fame  of  the  loadstone  and  of 
amber  in  the  writings  of  the  learned :  many  philosophers  cite 
the  loadstone  and  also  amber  whenever,  in  explaining  mysteries, 
their  minds  become  obfuscated  and  reason  can  no  farther  go.' 
Over-inquisitive  theologians,  too,  seek  to  light  up  God's  mys- 
teries and  things  beyond  man's  understanding  by  means  of 
the  loadstone  and  amber:  just  as  light-headed  metaphysicians, 
when  they  utter  and  teach  their  vain  imaginings,  employ  the 
loadstone  as  a  sort  of  Delphic  sword  and  as  an  illustration  of 
all  sorts  of  things.  Medical  men  also  (at  the  bidding  of  Galen), 
in  proving  that  purgative  medicines  exercise  attraction  through 
likeness  of  substance  and  kinships  of  juices  (a  silly  error  and 
gratuitous !),  bring  in  as  a  witness  the  loadstone,  a  substance 

^  Dr.  Wm.  Whewell  remarks  that  the  manner  in  which  Gilbert  expresses 
himself  shows  us  how  mysterious  the  fact  of  attraction  then  appeared,  so  that, 
as  he  says,  "  the  magnet  and  amber  were  called  in  aid  by  philosophers  as 
illustrations,  when  our  sense  is  in  the  dark  in  abstruse  inquiries;  and  when  our 
reason  can  go  no  further"  ("  Hist,  of  Ind.  Sc",  1859,  Vol.  II,  page  192). 


MAGNETIC  COITION,  ^$ 

cf  great  authority  and  of  noteworthy  efficiency,  and  a  body  of 
no  common  order.  Thus  in  very  many  affairs  persons  who 
plead  for  a  cause  the  merits  of  whicli  they  cannot  set  fortli, 
bring  in  as  masked  advocates  the  loadstone  and  amber.  But 
all  these,  besides  sharing  the  general  misapprehension,  are 
ignorant  that  the  causes  of  the  loadstone's  movements  are 
very  different  from  those  which  give  to  amber  its  properties ; 
hence  they  easily  fall  into  errors,  and  by  their  own  imaginings 
are  led  farther  and  farther  astray.  For  in  other  bodies  is  seen 
a  considerable  power  of  attraction,  differing  from  that  of  the 
loadstone, — in  amber,  for  example.  Of  this  substance  a  few 
words  must  be  said,  to  show  the  nature  of  the  attachment  of 
bodies  to  it,  and  to  point  out  the  vast  difference  between  this 
and  the  magnetic  actions;  for  men  still  continue  in  ignorance, 
and  deem  that  inclination  of  bodies  to  amber  to  be  an  attrac- 
tion, and  comparable  to  the  magnetic  coition.  The  Greeks  call 
this  substance  t/XeKzpor,  because,  when  heated  by  rubbing,  it 
attracts  to  itself  chaff ;  whence  it  is  also  called  aprta^,  and 
from  its  golden  color,  jpi»o-o0opon'  But  the  Moors  call  it 
carabe,  because  they  used  to  offer  it  in  sacrifices  and  in  the 


'  The  ancients  were  acquainted  with  but  two  electrical  bodies — amber, 
(electron),  which  has  given  the  denomination  of  the  science;  and  lyncurium, 
which  is  either  the  tourmaline  or  the  topaz  (Dr.  Davy,  "  Mem.  Sir  Hum. 
Davy,"  1836,  Vol.  I,  page  309).  From  a  recent  article  treating  of  gems,  the 
following  is  extracted:  The  name  of  the  precious  stone  inserted  in  the  ring  of 
Gyges  has  not  been  handed  down  to  us,  but  it  is  probable  that  it  was  the  topaz, 
whose  wonders  Philostrates  recounts  in  the  life  of  Apollonius.  An  attribute  o^ 
the  sun  and  of  fire,  the  ancients  called  it  the  gold  magnet,  as  it  was  credited 
with  the  power  of  attracting  that  metal,  indicating  its  veins,  and  discovering 
treasures.  Heliodorus,  in  his  story  of  Theagenes  and  Caricles,  says  that  the 
topaz  saves  from  fire  all  those  who  wear  it,  and  that  Caricles  was  preserved  by 
a  topaz  from  the  fiery  vengeance  of  Arsaces,  Queen  of  Ethiopia.  This  stone 
was  one  of  the  first  talismans  that  Theagenes  possessed  in  Egypt.  The  topaz 
at  present  symbolizes  Christian  virtues,  faith,  justice,  temperance,  gentleness, 
clemency. 


76  WILLIAM  GILBERT. 

worship  of  the  gods;  for  in  Arabic  carab  means  oblation,  not 
rapiens  paleas  (snatching  chaff),  as  Scaliger  would  have  it, 
quoting  from  the  Arabic  or  Persian  of  Abohali  (Hali  Abbas).' 
Many  call  this  substance  ambra  (amber),  especially  that  which 
is  brought  from  India  and  Ethiopia."  The  Latin  name  succi- 
num  appears  to  be  formed  from  succus,  juice.^  The  Suda- 
vienses  or  Sudini  call  the  substance  geniter,  as  though  genitmn 
terra  (produced  by  the  earth).  The  erroneous  opinion  of  the 
ancients  as  to  its  nature  and  source  being  exploded,  it  is 
certain  that  amber  comes  for  the  most  part  from  the  sea :  it  is 
gathered  on  the  coast  after  heavy  storms,  in  nets  and  through 
other  means,  by  peasants,  as  by  the  Sudini  of  Prussia ;  it  is 
also  sometimes  found  on  the  coast  of  our  own  Britain.  But  it 
seems  to  be  produced  in  the  earth  and  at  considerable  depth 
below  its  surface,  like  the  rest  of  the  bitumens  ;  then  to  be 
washed  out  by  the  sea-waves,  and  to  gain  consistency  under 
the  action  of  the  sea  and  the  saltness  of  its  waters.  For  at 
first  it  was  a  soft  and  viscous  matter,  and  hence  contains, 
buried  in  its  mass  forevermore  {csternis  sepulchris  relucentes), 
but  still  (shining)  visible,  flies,  grubs,  midges,  and  ants.  The 
ancients  as  well  as  moderns  tell  (and  their  report  is  confined 
by  experience)  that  amber  attracts  straws  and  chaff.  The 
same  is  done  by  jet,  a  stone  taken  out  of  the  earth  in  Britain, 
Germany,  and  many  other  regions :  it  is  a  hard  concretion  of 
black  bitumen, — a  sort  of  transformation  of  bitumen  to  stone. 


»  Salmasius  says  that  the  word  karabe,  the  Arabian  word  for  amber, 
signifies  the  power  of  attracting  straws.  (Note,  first  page  article  "  Electricity  " 
in  the  Encyclopaedia  Britannica.) 

"^  Consult  the  very  interesting  tables  given  by  Joannes  Zahn,  at  page  51, 
Chap.  VII,  Vol.  II,  of  his  "Specula  physico-raathematico-historica  notabi- 
lium. . .  .",  Norimbergse  1696. 

3  Pliny  considers  amber  as  the  juice  of  a  tree  concreted  into  a  solid  form 
(Dr.  Thos.  Thomson,  "Hist,  of  Chem.",  1830,  Vol.  I,  page  loi). 


MAGNETIC  COITION.  77 

Many  modern  authors  have  written  about  amber  and  jet  as 
attracting  chaff  and  about  other  facts  unknown  to  the  gen- 
erality, or  have  copied  from  other  writers :  with  the  results  of 
their  labors  booksellers'  shops  are  crammed  full.  Our  gen- 
eration has  produced  many  volumes  about  recondite,  abstruse, 
and  occult  causes  and  wonders,  and  in  all  of  them  amber  and 
jet  are  represented  as  attracting  chaff ;  but  never  a  proof  from 
experiments,  never  a  demonstration  do  you  find  in  them/ 
The  writers  deal  only  in  words  that  involve  in  thicker  dark- 
ness subject-matter  ;  they  treat  the  subject  esoterically,  mir- 
acle-mongeringly,  abstrusely,  reconditely,  mystically.  Hence 
such  philosophy  bears  no  fruit ;  for  it  rests  simply  on  a  few 
Greek  or  unusual  terms — just  as  our  barbers  toss  off  a  few 
Latin  words  in  the  hearing  of  the  ignorant  rabble  in  token  of 
their  learning,  and  thus  win  reputation — bears  no  fruit,  be- 
cause few  of  the  philosophers  themselves  are  investigators,  or 
have  any  first-hand  acquaintance  with  things ;  most  of  them 
are  indolent  and  untrained,  add  nothing  to  knowledge  by  their 
writings,  and  are  blind  to  the  things  that  might  throw  a  light 
upon  their  reasonings.  For  not  only  do  amber  and  (gagates 
or)  jet,^  as  they  suppose,  attract  light  corpuscles  (substances) : 
the  same  is  done  by  diamond,  sapphire,  carbuncle,  iris  stone,* 
opal,  amethyst,  vincentina,  English  gem  (Bristol  stone,  bris- 
tola),   beryl,    rock   crystal.''      Like   powers    of   attracting   are 

^  "  Stuffed  the  booksellers'  shops  by  copying  from  one  another  extrava- 
gant stories  concerning  the  attraction  of  magnets  and  amber  without  giving  any 
reason  from  experiment"  (Dr.  Wm.  Whewell,  "  Hist,  of  Ind.  Sciences,"  1859, 
Vol.  II,  page  192). 

'  The  gagates,  from  the  account  given  of  it  by  Pliny,  was  obviously  pit- 
coal  or  jet  (Thomson's  Chemistry,  Vol.  I,  page  loi).  Cardan  states,  Gagates  non 
lapis  est  (Lugduni  ed.  1663,  Vol.  X,  page  528). 

'''  Sir  David  Brewster  was  the  discoverer  of  the  pyro-electrical  condition 
of  the  diamond,  the  garnet,  the  amethyst,  etc.  See  Mottelay's  "  Chronological 
History"  at  A.D.  1717  and  1820,  and  the  references  to  rock-crystal,  etc., 
throughout  the  remainder  of  present  chapter. 


78  WILLIAM  GILBERT. 

possessed  by  glass,  especially  clear,  brilliant  glass ;  by  artificial 
gems  made  of  (paste)  glass  or  rock  crystal,  antimony  glass, 
many  fluor-spars,  and  belemnites.  Sulphur  also  attracts,  and 
likewise  mastich,  and  sealing-wax  [of  lac],  hard  resin,  orpiment 
(weakly).'  Feeble  power  of  attraction  is  also  possessed  in 
favoring  dry  atmosphere  by  sal  gemma  [native  chloride  of 
sodium],  mica,  rock  alum.*  This  we  may  observe  when  in 
mid-winter  the  atmosphere  is  very  cold,  clear,  and  thin ;  when 
the  electrical  ef^uvia  of  the  earth  offer  less  impediment,  and 
*  electric  bodies  are  harder:  of  all  this  later.  These  several 
bodies  (electrics)  not  only  draw  to  themselves  straws  and  chaff, 
but  all  metals,  wood,  leaves,  stones,  earths,  even  water  and  oil ; 
in  short,  whatever  things  appeal  to  our  senses  or  are  solid  : 
yet  we  are  told  that  it  attracts  nothing  but  chaff  and  twigs. 
Hence  Alexander  Aphrodiseus  incorrectly  declares  the  ques- 
tion of  amber  to  be  unsolvable,  because  that  amber  does 
attract  chaff,  yet  not  the  leaves  of  basil ;  but  such  stories  are 

^  Whewell  quotes:  "Not  only  amber  and  agate  attract  small  bodies,  as 
some  think,  but  diamond,  sapphire,  carbuncle,  opal,  amethyst,  Bristol  gem, 
beryl,  crystal,  glass,  glass  of  antimony,  spar  of  various  kinds,  sulphur,  mastic, 
sealing-wax  ;"  and  adds  that  Gilbert  mentioned  other  substances  ("  Hist.  Ind. 
Sc",  1859,  Vol.  II,  page  192), 

2  The  passage  is  thus  rendered  by  Humboldt:  "The  force  of  attraction 
belongs  to  a  whole  class  of  very  different  substances,  as  glass,  sulphur,  sealing- 
wax,  and  all  resinous  substances,  rock  crystal,  and  all  precious  stones,  alum, 
and  rock  salt"  ("  Cosmos,"  1849,  Vol.  II,  page  726). 

Dr.  Thos.  Brown  says  {Psetcdoloxia  Epidemica,  1658,  page  87):  "Unto  these 
Cabeus  addeth  white  Wax,  Gum  Elimi,  Gum  Guaici,  Pix  Hispanica  and 
Gipsum.  And  unto  these  we  add  Gum  Anine,  Benjamin,  Talcum,  Chyna- 
dishes,  Sandaraca,  Turpentine,  Styrax  Liquida,  and  Caranna  dried  into  a  hard 
consistence.  .  .  ."  (Dantzick  Memoirs,  Vol.  I,  page  180).  To  Dr.  Gilbert's  list 
of  electrics  Robert  Boyle  added  the  resinous  cake  which  remained  after  evapo- 
rating one-fourth  part  of  good  oil  of  turpentine;  the  dry  mass  which  remains 
after  distilling  a  mixture  of  petroleum  and  strong  spirits  of  nitre,  glass  of  anti- 
mony, glass  of  lead,  caput  mortuum  of  amber,  white  sapphire,  white  amethyst, 
diaphanous  ore  of  lead,  carnelian,  and  a  green  stone  supposed  to  be  a  sapphire 
(art.  "Electricity,"  Ency.  Brit.). 


MAGNETIC  COITION.  79 

false,  disgracefully  inaccurate.'  Now  in  order  clearly  to 
understand  by  experience  how  such  attraction  takes  place,  and 
what  those  substances  may  be  that  so  attract  other  bodies 
(and  in  the  case  of  many  of  these  electrical  substances,  though 
the  bodies  influenced  by  them  lean  toward  them,  yet  because 
of  the  feebleness  of  the  attraction  they  are  not  drawn  clean  up 
to  them,  but  are  easily  made  to  rise),  make  yourself  a  rotating- 
needle  (electroscope — versorium)  of  any  sort  of  metal,'^  three 
or  four  fingers  long,  pretty  light,  and  poised  on  a  sharp  point 
after  the  manner    of   a  magnetic    pointer.      Bring    near    to 


one  end  of  it  a  piece  of  amber  or  a  gem,  lightly  rubbed, 
polished  and  shining :  at  once  the  instrument  revolves.  Several 
objects  are  seen  to  attract  not  only  natural  objects,  but  things 
artificially  prepared,  or  manufactured,  or  formed  by  mixture. 
Nor  is  this  a  rare  property  possessed  by  one  object  or  two  (as 
is  commonly  supposed),  but  evidently  belongs  to  a  multitude 
of  objects,  both  simple  and  compound,  e.g.,  seaHng-wax  and 
other  unctuous  mixtures.     But  why  this  inclination  and  what 


'  When  amber  has  been  rubbed,  many  "  particles  of  matter,  like  so  many 
fine  threads,  too  small  to  be  seen,  come  out  of  it,  and  dart  themselves  into  the 
air,  where  meeting  with  small  bodies,  they  get  into  the  pores  of  them,  and 
then  return  back  into  the  amber;  at  the  same  time  the  air  continually  repelling 
these  small  threads,  and  forcing  them  to  contract  themselves  into  less  and  less 
compass,  presses  likewise  in  the  same  manner  upon  the  light  bodies  into  the 
pores  of  which  these  small  threads  have  thrust  themselves;  so  that  in  returning 
back  to  the  amber  they  carry  small  straws,  in  whose  pores  they  are  engaged 
along  with  them  "  (Rohault's  "System  of  Nat.  Phil.",  London  1728,  page  187; 
Rohaulti  Physica,  London  1718,  Par,  III,  Cap.  VIII,  page  408). 

'  See  note  5,  page  xxxi. 


8o  WILLIAM  GILBERT. 

these  forces, — on  which  points  a  few  writers  have  given  a  very 
small  amount  of  information,  while  the  common  run  of  phi- 
losophers give  us  nothing, — these  questions  must  be  considered 
fully.  Galen  recognizes  in  all  three  kinds  of  attractions  in 
nature :  first,  the  attraction  exercised  by  those  bodies  which 
attract  by  an  elemental  quality — heat,  to  wit ;  secondly,  by 
those  which  attract  by  the  in-rush  into  a  vacuum. ;  thirdly,  by 
those  which  attract  through  a  property  pertaining  to  their 
entire  mass:  and  these  three  kinds  are  enumerated  by  Avi- 
cenna  and  others.  This  division  cannot  by  any  means  content 
us,  nor  does  it  define  the  causes  {causas)  of  amber,  jet,  diamond, 
and  other  like  substances,  which  owe  to  the  same  virtue  the 
forces  they  possess ;  nor  of  loadstone  or  of  other  magnetic 
bodies,  which  possess  a  force  altogether  different  from  that  of 
those  other  bodies,  both  in  its  efficiency  and  in  the  sources 
whence  it  is  derived.  We  must,  therefore,  find  other  causes 
of  movements,  or  must  with  these  stray  about  as  it  were  in 
darkness,  never  at  all  reaching  our  goal.  Now  amber  does  not 
*  attract  by  heat,  for  when  heated  at  a  fire  and  brought  near  to 
straws,  whether  it  is  merely  warm,  or  whether  it  is  hot,  even 
burning  hot,  or  even  brought  to  the  flaming  point,  it  has  no 
attraction.  Cardan  (and  Pictorius  too)  is  of  opinion  that  the 
attraction  of  amber  is  much  like  that  seen  in  the  cupping-glass : 
yet  the  attractional  force  of  the  cupping-glass  does  not  really 
come  from  igneous  force ;  but  he  had  already  said  that  a  dry 
body  is  eager  to  drink  up  one  that  is  moist  and  juicy,  and 
therefore  such  bodies  are  drawn  to  it.  These  two  explications 
are  inconsistent,  and  they  are  without  ground  in  reason  also. 
For  were  amber  to  move  toward  its  sustenance,  or  other  bodies 
to  turn  to  amber,  as  to  their  food,  the  one,  being  swallowed  up, 
would  disappear,  while  the  other  would  increase  in  size.  And 
then  why  seek  in  amber  the  attractive  force  of  fire?     If  fire 


MAGNETIC  COITION.  51 

attracts,  why  do  not  many  other  bodies  heated  by  the  fire, 
the  sun,  or  by  friction  attract  also?  Nor  can  attraction,  be- 
cause of  air  displaced,  occur  in  open  air,  though  this  is  the 
cause  Lucretius  assigns  for  magnetic  movements ;  nor  in  the 
cupping-glass  can  heat  or  fire  feeding  on  the  air  attract :  the 
air  in  the  cupping-glass  rarefied  to  flame,  when  again  it  be- 
comes dense  and  is  compressed  into  small  space,  causes  the 
skin  and  flesh  to  rise,  because  nature  avoids  a  vacuum.  In 
open  air,  heated  objects  cannot  attract,  not  even  metals  or 
stones  brought  to  a  very  high  temperature  by  fire.  For  an 
iron  rod  at  white  heat,  a  flame,  a  candle,  a  flaming  torch,  or  a^ 
red-hot  coal  when  brought  near  to  straws  or  to  a  revolving 
pointer  [versoriiini)  does  not  attract ;  and  yet  plainly  all  these 
cause  the  air  to  come  to  them  in  a  current,  for  they  consume 
air  as  a  lamp  consumes  oil.  But  of  heat,  and  how  very  different 
is  the  view  held  by  the  whole  crowd  of  the  philosophers,  as  to 
its  attractive  power  in  natural  bodies  and  materia  medica,  from 
the  fact  as  seen  in  nature,  we  will  treat  elsewhere  when  we 
come  to  explain  what  heat  and  cold  really  are.  They  are 
very  general  properties  or  close  appurtenances  of  substances, 
but  are  not  called  true  causes ;  and  if  I  may  use  the  expres- 
sion, they  utter  certain  words,  but  in  fact  they  show  nothing 
specifically.  Nor  does  the  supposed  attractive  force  of  amber 
arise  from  any  peculiar  property  of  its  substance  or  from  any 
special  relation  between  it  and  other  bodies ;  for  in  many  other 
substances,  if  we  but  search  with  any  diligence,  we  see  the 
same  effect,  and,  by  them,  all  other  bodies,  of  whatever  proper- 
ties possessed,  are  attracted.  And  likeness  is  not  the  cause  of 
amber's  attracting,  for  all  things  that  we  see  on  the  globe, 
whether  similar  or  dissimilar,  are  attracted  by  amber  and  such 
like  ;  hence  no  strong  analogy  is  to  be  drawn  either  from  like- 
ness or  from  identity  of  substance.     Besides,  like  does  not 


82  WILLIAM   GILBERT. 

attract  like — a  stone  does  not  attract  a  stone,  flesh  flesh :  there 
is  no  attraction  outside  of  the  class  of  magnetic  and  electric 
bodies.  Fracastorio  thinks  that  all  bodies  that  mutually  at- 
tract are  alike,  or  of  the  same  species,  and  that,  either  in  their 
action  or  in  their  proper  subjectutn :  "  now  the  proper  sub- 
fectum"  says  he,  "  is  that  from  which  is  emitted  that  emana- 
tional  something  which  attracts,  and,  in  mixed  substances,  this 
is  not  perceptible  on  account  of  deformation,  whereby  they 
are  one  thing  actu,  another  potentid.  Hence,  perhaps,  hairs 
and  twigs  are  drawn  to  amber  and  diamond  not  because  they 
are  hairs,  but  because  there  is  imprisoned  within  them  either 
air  or  some  other  principle  that  is  first  attracted  and  that  has 
reference  and  analogy  to  that  which  of  itself  attracts ;  and 
herein  amber  and  diamond  are  as  one,  in-  virtue  of  a  principle 
common  to  both."  So  much  for  Fracastorio.  But  had  he  in 
experiment  noted  that  all  bodies  are  attracted  by  electrics  save 
those  which  are  afire  or  flaming,  or  extremely  rarefied,  he 
never  would  have  entertained  such  views.  Men  of  acute  in- 
telligence, without  actual  knowledge  of  facts,  and  in  the 
absence  of  experiment,  easily  slip  and  err.  In  greater  error 
are  they  who  hold  amber,  diamond,  etc.,  and  the  objects 
attracted  by  them,  to  be  like  one  another,  but  not  the  same, 
near  to  one  another  in  kind,  and  that  therefore  like  moves 
toward  like,  and  is  by  it  perfected.  But  that  is  reckless  specu- 
lation ;  for  all  bodies  are  drawn  to  all  electrics,  save  bodies 
aflame  or  too  rarefied,  as  the  air  which  is  the  universal  effluvium 
of  the  globe.  Plants  draw  moisture,  and  thus  our  crops  thrive 
and  grow ;  but  from  this  analogy  Hippocrates  in  his  book  De 
Natura  Hominis,  L,  illogically  infers  that  morbid  humor  is 
purged  by  the  specific  virtue  of  a  drug.  Of  the  action  of 
purges  we  will  treat  elsewhere.  Wrongly,  too,  attraction  is 
postulated  to  exist  in  other  effects ;    e.g.,  when  a  stoppered 


MAGNETIC  COITION.  83 

bottle  of  water  being  covered  with  a  heap  of  wheat,  its  liquid 
is  drawn  out ;  for  in  fact  the  liquid  is  reduced  to  vapor  by  the 
spirit  of  the  fermenting  wheat,  and  .the  wheat  takes  in  that 
vapor.  Nor  do  elephants'  tusks  suck  up  moisture,  but  trans- 
form it  into  vapor  and  absorb  it.  And  thus  very  many  bodies 
are  said  to  attract,  whereas  the  ground  of  their  action  is  to  be 
sought  elsewhere.  A  large  polished  lump  of  amber  attracts ; 
a  smaller  piece,  or  a  piece  of  impure  amber,  seems  not  to 
attract  without  friction.  But  very  many  electric  bodies  (as 
precious  stones,  etc.)  do  not  attract  at  all  unless  they  are  first 
rubbed  ;  while  sundry  other  bodies,  and  among  them  some 
gems,  have  no  power  of  attraction,  and  cannot  be  made  to 
attract,  even  by  friction ;  such  bodies  [anelectrics — non-elec- 
trics] are  emerald,  agate,  carnelian,'  pearls,  jasper,  chalcedony, 
alabaster,  porphyry,  coral,  the  marbles,  lapis  lydius  (touch- 
stone, basanite),  flint,  bloodstone,  emery  or  corundum  {tnugris), 
bone,  ivory;  the  hardest  woods,  as  ebony;  some  other  woods, 
as  cedar,  juniper,  cypress ;  metals,  as  silver,  gold,  copper,  iron. 
The  loadstone,  though  it  is  susceptible  of  a  very  high  polish, 
has  not  the  electric  attraction.  On  the  other  hand,  many 
bodies  (already  mentioned)  that  can  be  polished  attract  when 
rubbed.  All  this  we  shall  understand  when  we  have  more 
closely  studied  the  prime  origin  of  bodies.  As  is  plain  to  all, 
the  earth's  mass  or  rather  the  earth's  framework  and  its  crust 
consist  of  a  twofold  matter,  a  matter,  to  wit,  that  is  fluid  and 
liumid,  and  a  matter  that  is  firm  and  dry.  From  this  two- 
old  matter,  or  from  the  simple  concretion  of  one  of  these 
matters,  come  all  the  bodies  around  us,  which  consist  in  major 
proportion  now  of   terrene    matter,  anon   of  watery.     Those 

'  Sarda  was  the  name  of  carnelian,  so  called  because  it  was  first  found 
near  Sardis.  The  sardonyx  was  also  another  name  for  carnelian  (Dr.  Th. 
Thomson's  "Chemistry,"  1830,  Vol.  I,  page  100). 


84  WILLIAM   GILBERT. 

that  derive  their  growth  mainly  from  humors,  whether  watery 
humor  or  one  more  dense ;  or  that  are  fashioned  from  these 
humors  by  simple  concretion,  or  that  were  concreted  out  of 
them  long  ages  ago  ;  if  they  possess  sufiicient  firmness,  and 
after  being  polished  are  rubbed,  and  shine  after  friction, — such 
substances  attract  all  bodies  presented  to  them  in  the  air, 
unless  the  said  bodies  be  too  heavy.  For  amber  and  jet  are 
concretions  of  water ;  so  too  are  all  shining  gems,  as  rock- 
crystal,  which  is  a  product  of  limpid  water,  not  always  of  such 
water  at  an  extremely  low  temperature,  as  some  have  thought, 
but  sometimes  at  a  more  moderate  degree  of  cold,  the  nature 
of  the  ground  fashioning  them,  and  the  humor  or  juices  being 
prisoned  in  definite  cavities,  just  as  fluorites  are  generated  in 
mines.  So  clear  glass  is  reduced  from  sand  and  other  sub- 
stances that  have  their  origin  in  humid  juices.  But  these 
*  substances  contain  a  quantity  of  impurities  of  metals,  or 
metals  themselves,  stones,  rocks,  wood,  earth,  or  are  largely 
mixed  with  earth ;  therefore  they  do  not  attract.  Rock  crys- 
tal, mica,  glass,  and  other  electric  bodies  do  not  attract  if  they 
be  burned  or  highly  heated,  for  their  primordial  humor  is  de- 
stroyed by  the  heat,  is  altered,  and  discharged  as  vapor.  Hence 
all  bodies  that  derive  their  origin  principally  from  humors,  and 
that  are  firmly  concreted,  and  that  retain  the  appearance  and 
property  of  fluid  in  a  firm,  solid  mass,  attract  all  substances, 
whether  humid  or  dry.  Such  as  are  parts  of  the  true  sub- 
stance of  the  earth  or  differ  but  little  from  that,  appear  to 
attract  also,  but  in  a  very  different  way,  and,  so  to  speak,  mag- 
netically :  of  them  we  are  to  treat  later.  But  those  that  con- 
sist of  mixed  water  and  earth,  and  that  result  from  equal  deg- 
radation of  both  elements — in  which  the  magnetic  force  of 
the  earth  is  degraded  and  lies  in  abeyance,  while  the  aqueous 
humor,  spoilt  by  combination  with  a  quantity  of  earth,  does  not 


MAGNETIC  COITION.  85 

form  a  concretion  by  itself,  but  mingles  with  the  earthy  matter 
— such  bodies  are  powerless  to  attract  to  themselves  aught 
that  they  are  not  in  actual  contact  with,  or  to  repel  the  same. 
For  this  reason  it  is  that  neither  metals,  marbles,  flints,  woods, 
grasses,  flesh,  nor  various  other  substances  can  attract  or 
solicit  a  body,  whether  magnetically  or  electrically  (for  it 
pleases  us  to  call  electric  force  that  force  which  has  its  origin* 
in  humors).  But  bodies  consisting  mostly  of  humor  and  not 
firmly  compacted  by  nature  wherefore  they  do  not  stand  fric- 
tion, but  either  fall  to  pieces  or  grow  soft,  or  are  sticky,  as 
pitch,  soft  rosin,  camphor,  galbanum,  ammoniacum,  storax, 
asa,  gum  benjamin,  asphaltum  (especially  in  a  warm  atmos- 
phere), do  not  attract  corpuscles.  For  without  friction  few 
bodies  give  out  their  true  natural  electric  emanation  and 
effluvium.  Turpentine  resin  in  the  liquid  state  does  not  at-* 
tract,  because  it  cannot  be  rubbed ;  but  when  it  hardens  to  a 
mastic  it  does  attract. 

And  now,  at  last,  we  have  to  see  why  corpuscles  are 
drawn  toward  substances  that  derive  their  origin  from  water, 
and  by  what  manner  of  force,  by  what  hands,  so  to  speak, 
such  substances  lay  hold  of  matters  nigh  them. 

In  all  bodies  everywhere  are  presented  two  causes  or  prin- 
ciples whereby  the  bodies  are  produced,  to  wit,  matter  {mate- 
ria) and  form  {forma).  Electrical  movements  come  from  the 
materia,  but  magnetic  from  the  prime  forma ;  and  these  two 
differ  widely  from  each  other  and  become  unlike, — the  one 
ennobled  by  many  virtues,  and  prepotent  ;  the  other  lowly,  of 
less  potency,  and  confined  in  certain  prisons,  as  it  were ; 
wherefore  its  force  has  to  be  awakened  by  friction  till  the  sub- 
stance attains  a  moderate  heat,  and  gives  out  an  effluvium, 
and  its  surface  is  made  to shi-ne.  Moist  air  blown  upon  it  from* 
the  mouth  or  a  current  of  humid  air  from  the  atmosphere 


86  WILLIAM  GILBERT. 

chokes  its  powers ;  and  if  a  sheet  of  paper  or  a  Hnen  cloth  be 
interposed  there  is  no  movement.  But  loadstone,  neither 
rubbed  nor  heated,  and  even  though  it  be  drenched  with 
liquid,  and  whether  in  air  or  water,  attracts  magnetic  bodies, 
and  that,  though  solidest  bodies  or  boards,  or  thick  slabs  of 
stone    or  plates   of   metal,  stand    between.      A  loadstone  at- 

*  tracts  only  magnetic  bodies ;  electrics  attract  everything.  A 
loadstone  lifts  great  weights ;  a  strong  one  weighing  two 
ounces  lifts  half  an  ounce  or  one  ounce.  Electrics  attract 
only  light  weights;  e.g.,  a  piece  of  amber  three  ounces  in 
weight  lifts  only  one-fourth  of  a  barleycorn's  weight. 

But  this  attraction  of  amber  and  of  electric  bodies  must  be 
investigated  further  ;  and  since  it  is  an  acquired  state  {affectio), 
the  question  arises  why  amber  is  rubbed,  and  what  state  is 
brought  about  by  rubbing ;  also,  what  causes  are  evoked  that 
seize  all  sorts  of  substances.  By  friction  it  is  made  moder- 
ately hot  and  also  smooth  ;  and  these  conditions  must  in  most 
cases  concur ;  but  a  large  polished  piece  of  amber  or  of  jet 
attracts  even  without  friction,  though  not  strongly ;  yet  if  it 

*  be  carefully  brought  nigh  to  a  flame  or  a  red  coal  and  warmed 
to  the  same  degree  as  by  friction,  it  does  not  attract  corpus- 
cles, because  it  becomes  involved  in  dark  fumes  from  the  body 
of  the  hot  or  flaming  mass,  which  emits  a  hot  exhalation  ;  and 
the  vapor  from  that  other  body  is  driven  upon  it — something 
quite  alien  to  the  nature  of  the  amber.  Besides,  the  exhalation 
produced  in  the  amber  by  an  alien  heat  is  feeble,  for  the  amber 
must  not  have  any  heat  save  that  produced  by  friction :  its 
own  heat,  so  to  speak, — not  heat  contributed  by  other  bodies. 
For  as  the  igneous  heat  emitted  by  any  flaming  matter  is  use- 

:« less  to  procure  for  electrics  their  virtue,  so,  too,  heat  from  the 
sun's  rays  does  not  excite  an  electric  by  the  right  dissolution 
of  its  matter, — rather  dissipates  and  consumes  it  (albeit  a  body 


MAGNETIC  COITION,  8/ 

that  undergoes  friction  and  then  is  exposed  to  the  solar  rays 
retains  its  powers  longer  than  it  does  in  shade,  because  that  in 
shade  effluvia  are  condensed  more  and  more  quickly) ;  further,  * 
the  sun's  heat,  heightened  by  means  of  a  burning-glass,  im- 
parts no  power  to  amber,  for  it  dissipates  and  spoils  all  the 
electric  effluvia.  Again,  flaming  sulphur  and  burning  sealing- 
wax  do  not  attract,  for  heat  produced  by  friction  dissolves* 
bodies  into  effluvia,  and  these  are  consumed  by  flame.  It  is 
impossible  for  solid  electrics  to  be  resolved  into  their  effluvia 
otherwise  than  by  attrition,  save  a  few  that,  because  of  their 
native  strength,  emit  effluvia  continually.  They  are  to  be 
rubbed  with  bodies  that  do  not  foul  the  surface,  and  that 
cause  them  to  shine,  e.g.,  strong  silk,  and  coarse  woollen  cloth, 
scrupulously  clean,  and  the  dry  palm  of  the  hand.  Amber 
may  be  rubbed  with  amber,  with  diamond,  with  glass,  etc. 
Thus  are  electrics  made  ready  for  action. 

And  now  what  is  it  that  produces  the  movement  ?  The 
body  itself  circumscribed  by  its  contour  ?  Or  is  it  something 
imperceptible  for  us  flowing  out  of  the  substance  into  the 
ambient  air?  (This  appears  to  have  been  in  some  sense  the 
opinion  of  Plutarch,  who,  in  the  QucBstiones  Platonic(2,  says 
that  there  is  in  amber  something  flame-like,  or  having  the 
nature  of  the  breath,  and  that  this,  when  the  paths  are  cleared 
by  friction  of  the  surface,  is  emitted  and  attracts  bodies.) 
And  if  it  is  an  effluvium,  does  the  effluvium  set  the  air  in  cur- 
rent, and  is  the  current  then  followed  by  the  bodies  ?  or  is  it 
the  bodies  themselves  directly  that  are  drawn  up  ?  But  if  the 
amber  attracts  the  body  itself,  then  supposing  its  surface  is 
clean  and  free  from  adhesions,  what  need  is  there  of  friction? 
Nor  does  the  force  come  from  the  lustre  proceeding  from  the 
rubbed  and  polished  electric  ;  for  the  vincentina,  the  diamond, 
and  pure  glass  attract  when  they  are  rough,  but  not  so  strongly 


O'J  WILLIAM  GILBERT. 

nor  SO  readily ;  because  then  they  are  not  so  easily  cleansed 
of  extraneous  moisture  settled  on  the  surface,  nor  are  they  sub- 
jected all  over  to  such  an  equal  degree  of  friction  as  to  be 
resolved  into  effluvia.  Nor  does  the  sun,  with  its  shining  and 
its  rays,  which  are  of  vast  importance  in  nature,  attract  bodies 
thus ;  and  yet  the  common  run  of  philosophizers  think  that 
liquids  are  attracted  by  the  sun,  whereas  only  the  denser 
humors  are  resolved  into  rarer,  (and)  into  vapor  and  air ;  and 
thus,  through  the  motion  given  to  them  by  diffusion,  they 
ascend  to  the  upper  regions,  or,  being  attenuated  exhalations, 
are  lifted  by  the  heavier  air.  Neither  does  it  seem  that  the 
electric  attraction  is  produced  by  the  effluvia  rarefying  the  air 
so  that  bodies,  impelled  by  the  denser  air,  are  made  to  move 
toward  the  source  of  the  rarefaction  :  if  that  were  so,  then  hot 
bodies  and  flaming  bodies  would  also  attract  other  bodies  ; 
but  no  lightest  straw,  no  rotating  pointer  is  drawn  toward  a 
flame.  If  there  is  afflux  and  appulsion  of  air,  how  can  a  mi- 
nute diamond  of  the  size  of  a  chick-pea  pull  to  itself  so  much 
air  as  to  sweep  in  a  corpuscle  of  relatively  considerable 
length,  the  air  being  pulled  toward  the  diamond  only  from 
around  a  small  part  of  one  or  other  end  ?  Besides,  the  at- 
tracted body  must  stand  still  or  move  more  slowly  before 
coming  into  contact,  especially  if  the  attracting  body  be  a 
broad  flat  piece  of  amber,  on  account  of  the  heaping  up  of  air 
on  the  surface,  and  its  rebounding  after  collision.  And  if  the 
effluvia  go  out  rare  and  return  dense  (as  with  vapors),  then  the 
body  would  begin  to  move  toward  the  electric  a  little  after 
the  beginning  of  its  application  ;  yet,  when  rubbed  electrics 
*  are  suddenly  applied  to  a  versorium,  instantly  the  pointer 
turns,  and  the  nearer,  it  is  to  the  electric  the  quicker  is  the 
attraction.  But  if  rare  effluvia  rarefy  the  medium,  and  there- 
fore the  bodies  pass  from  a  denser  into  a  rarer  medium,  then 


MAGNETIC  COITION.  89 

the  bodies  might  be  attracted  sideways  or  downward,  but  not 
upward,  or  the  attraction  and  holding  of  the  bodies  would  be 
only  for  a  moment.  But  jet  and  amber  after  one  friction 
strongly  and  for  a  length  of  time  solicit  and  attract  bodies, 
sometimes  for  as  long  as  five  minutes,  especially  if  the  weather 
is  fair.  But  if  the  mass  of  amber  be  large,  and  its  surface 
polished,  it  attracts  without  friction.  Flint,  on  being  struck, 
gives  off  inflammable  matter  that  turns  to  sparks  and  heat. 
Hence  the  denser  fire-containing  efHuvia  of  flint  are  very 
different  indeed  from  the  electrical  effluvia,  which,  by  reason 
of  their  extreme  tenuity,  cannot  take  fire,  nor  are  they  fit 
matter  of  flame.  They  are  not  a  breath,  for,  when  given  forth, 
they  do  not  exert  propelling  force  ;  they  flow  forth  without 
any  perceptible  resistance,  and  reach  bodies.  They  are  ex- 
ceedingly attenuated  humors,  much  more  rarefied  than  the 
ambient  air ;  to  produce  them  requires  bodies  generated  of 
humor  and  consolidated  to  considerable  hardness.  Non-elec- 
tric bodies  are  not  resolvable  into  humid  effluvia  ;  and  such 
effluvia  mingle  with  the  common  and  general  effluvia  of  the 
earth,  and  are  not  peculiar.  In  addition  to  the  attracting  of 
bodies,  electrics  hold  them  for  a  considerable  time.  Hence  it* 
is  probable  that  amber  exhales  something  peculiar  that  attracts 
the  bodies  themselves,  and  not  the  air.  It  plainly  attracts  the 
body  itself  in  the  case  of  a  spherical  drop  of  water  standing 
on  a  dry  surface ;  for  a  piece  of  amber  held  at  suitable  dis- 
tance pulls  toward  itself  the  nearest  particles  and  draws  them  * 
up  into  a  cone  ;  were  they  drawn  by  the  air  the  whole  drop 
would  come  toward  the  amber.  And  that  amber  does  not 
attract  the  air  is  thus  proved  :  take  a  very  slender  wax  candle 
giving  a  very  small  clear  flame ;  bring  a  broad  flat  piece  of  :•= 
amber  or  jet,  carefully  prepared  and  rubbed  thoroughly,  with- 
in a  couple  of  fingers'  distance  from  it ;  now  an  amber  that 


90  WILLIAM  GILBERT. 

will  attract  bodies  from  a  considerable  radius  will  cause  no 
motion  in  the  flame,  though  such  motion  would  be  inevitable 
if  the  air  were  moving,  for  the  flame  would  follow  the  current 
of  air.  The  amber  attracts  from  as  far  as  the  effluvia  are  sent 
out ;  but  as  the  body  comes  nearer  the  amber  its  motion  is 
quickened,  the  forces  pulling  it  being  stronger,  as  is  the  case 
also  in  magnetic  bodies,  and  in  all  natural  motion  ;  and  the 
motion  is  not  due  to  rarefaction  of  the  air  or  to  an  action  of 
the  air  impelling  the  body  to  take  the  vacated  place  ;  for  in 
that  case  the  body  would  be  pulled  but  not  held,  since,  at  first, 
approaching  bodies  would  even  be  repelled  just  as  the  air  itself 
would  be :  yet  in  fact  the  air  is  not  in  the  least  repelled  even 
at  the  instant  that  the  rubbed  amber  is  brought  near  after 
very  rapid  friction.  An  effluvium  is  exhaled  by  the  amber 
and  is  sent  forth  by  friction  ;  pearls,  carnelian,  agate,  jasper, 
chalcedony,  coral,  metals,  and  the  like,  when  rubbed  are  inac- 
tive ;  but  is  there  nought  that  is  emitted  from  them  also  by 
heat  and  friction  ?  There  is  indeed ;  but  what  is  emitted 
from  the  denser  bodies,  and  those  with  considerable  admix- 
ture of  earth  matter,  is  thick  and  vaporous  ;  and  in  fact  in  the 

*  case  of  very  many  of  the  electric  bodies,  if  they  be  violently 
rubbed,  there  is  but  a  faint  attraction  of  bodies  to  them,  or 
none  at  all ;  the  best  method  is  to  use  gentle  but  very  rapid 
friction,  for  so  the  finest  effluvia  are  elicited.  The  effluvia 
arise  from  a  subtle  solution  of  moisture,  not  from  force  ap- 
plied violently  and  recklessly ;  this  is  true  especially  of  bodies 
that  are  of  oily  substance  consolidated,  which,  when  the  at- 
mosphere is  thin  and  the  wind  is  from  the  north,  or  here  in 

*  England  from  the  east,  produce  their  effects  best  and  with 
most  certainty ;  but  in  a  south  wind  and  a  humid  atmosphere 
the  effect  is  very  slight :  so  that  effluvia  that  attract  but  feebly 
when  the  weather  is  clear,  produce  no  motion  at  all  when  it  is 


MAGNETIC  COITION.  9 1 

cloudy.  And  this  as  well  because  in  thick  weather  light 
objects  are  harder  to  move,  as  also  (and  rather)  because  the 
effluvia  are  stifled,  and  the  surface  of  the  rubbed  body  is 
affected  by  the  vaporous  air,  and  the  effluvia  are  stopped  at 
their  very  origin  ;  hence  it  is  that  in  amber,  jet,  and  sulphur, 
because  these  bodies  do  not  so  readily  collect  the  humid  air  on 
their  surface,  and  are  much  more  thoroughly  resolved,  this 
force  is  not  so  easily  suppressed  as  in  gems,  rock-crystal,  glass, 
and  the  like,  which  collect  the  condensed  moist  air  on  their 
surface.  But  the  question  may  arise,  why  amber  attracts 
water,  though  water  existing  on  a  surface  annuls  its  action. 
That  is  because  it  is  one  thing  to  suppress  the  effluvium  at  its 
rise,  another  to  destroy  it  after  it  is  emitted.  Thus  a  certain* 
gauzy  texture  of  silk,  commonly  called  sarsnet,  when  quickly 
laid  over  amber  immediately  after  friction,  hinders  the  body's* 
attraction ;  but  if  it  be  interposed  midway  between  the  two 
bodies,  it  does  not  altogether  annul  the  attraction.  Moisture 
from  steam,  a  breath  from  the  mouth,  water  thrown  on  the 
amber,  instantly  check  the  effluvium.  But  olive-oil  that  is* 
light  and  pure  does  not  prevent  it,  and  even  rubbing  amber* 
with  a  warm  finger  dipped  in  the  oil  does  not  prevent  attraction. 
But  if  after  that  friction  the  amber  be  drenched  with  alcohol, 
or  brandy,  it  does  not  attract,  as  the  spirit  is  heavier,  denser, 
than  the  oil,  and  when  added  to  the  oil  sinks  below  it.  For 
olive-oil  is  light  and  rare,  and  does  not  oppose  the  passage  of 
the  lightest  effluvia.  A  breath,  then,  proceeding  from  a  body 
that  is  a  concretion  of  moisture  or  aqueous  fluid,  reaches  the 
body  that  is  to  be  attracted,  and  as  soon  as  it  is  reached  it  is 
united  to  the  attracting  electric ;  and  a  body  in  touch  with 
another  body  by  the  peculiar  radiation  of  effluvia  makes  of  the 
two  one:  united,  the  two  come  into  most  intimate  harmony, 
and  that    is  what  is  meant  by  attraction.     This  unity  is,  ac- 


92  WILLIAM  GILBERT. 

cording  to  Pythagoras,  the  principle,  through  participation,  in 
which  a  thing  is  said  to  be  one.  For  as  no  action  can  be  per- 
formed by  matter  save  by  contact,  these  electric  bodies  do 
not  appear  to  touch,  but  of  necessity  something  is  given  out 
from  the  one  to  the  other  to  come  into  close  contact  there- 
with, and  be  a  cause  of  incitation  to  it. 

All  bodies  are  united  and,  as  it  were,  cemented  together  by 
moisture,  and  hence  a  wet  body  on  touching  another  body 
attracts  it  if  the  other  body  be  small ;  and  wet  bodies  on  the 
surface  of  water  attract  wet  bodies.  But  the  peculiar  effluvia 
of  electrics,  being  the  subtilest  matter  of  solute  moisture, 
attract  corpuscles.'  Air,  too  (the  earth's  universal  effluvium), 
unites  parts  that  are  separated,  and  the  earth,  by  means  of 
the  air,  brings  back  bodies  to  itself ;  else  bodies  would  not  so 
eagerly  seek  the  earth  from  heights.  The  electric  efHuvia 
differ  much  from  air,  and  as  air  is  the  earth's  effluvium,  so  elec- 
tric bodies  have  their  own  distinctive  effluvia ;  and  each  pecu- 
liar effluvium  has  its  own  individual  power  of  leading  to  union, 
its  own  movement  to  its  origin,  to  its  fount,  and  to  the  body 
that  emits  the  effluvium.  But  bodies  that  give  out  a  thick  or 
a  vaporous  or  an  aerial  effluvium  when  rubbed  have  no  effect ; 
for  either  such  effluvia  are  diverse  from  humor  (unifier  of  all 
things),  or,  being  very  like  the  common  air,  they  become 
blended  with  the  air  and  one  with  it :  wherefore  they  have 
no  effect  in  the  air,  and  do  not  produce  any  movements  dif- 
ferent from  those  of  that  universal  and  common  element. 
*  Bodies  tend  to  come  together  and  move  about  on  the  surface 
of  water  like  the  rod   C,  which  dips  a  little  into  the   water. 


'  Consult  Robert  Boyle's  "Of  the  Strange  Subtilty  of  EfBuviums,"  1673, 
pages  38-42,  52,  53  ;  "  Of  the  Great  Efficacy  of  Effluviums,"  1673,  pages 
18,  19,  32,  33;  "Of  the  Determinate  Nature  of  Effluviums,"  1673,  pages  21,  57; 
"  An  Essay  about Gems,"  1672,  pages  108-112. 


MAGNETIC  COITION. 


93 


Evidently  the  rod  EF,  floated  by  the  cork  H  and  having  only 
the  wetted  end  F  above  the  water's  surface,  will  be  attracted 
by  the  rod  C,  if  C  be  wetted  a  Httle  above  the  water's  surface. 


As  a  drop  brought  into  contact  with  another  drop  is  attracted, 
and  the  two  forthwith  unite,  in  the  same  way  a  wet  object  on 
the  surface  of  water  seeks  union  with  another  wet  object  when 
the  surface  of  the  water  rises  in  both  :  at  once,  like  drops  or 
bubbles  of  water,  they  ccme  together ;  but  they  are  in  much 
nigher  neighborhood  than  in  the  case  of  electrics,  and  they 
unite  by  their  wetted  surfaces.  But  if  the  whole  rod  C  be 
dry  above  the  water,  it  no  longer  attracts  but  repels  the  rod 
EF.  The  same  is  seen  in  the  case  of  bubbles  on  water :  one 
is  seen  to  approach  another,  all  the  more  rapidly  the  nearer 
they  are.  Solids  draw  to  solids  through  the  medium  of  liquid  ; 
ie.g.,  touch  the  end  of  a  versorium  with  the  end  of  a  rod  on , 
which  a  drop  of  water  stands :  the  instant  the  rotating  pointer 
comes  in  contact  with  the  circumference  of  the  drop  it  ad- 
heres to  it  with  a  sudden  motion.  So  do  bodies  concreted 
from  liquids  when  melted  a  little  in  the  air  exercise  attraction, 
their  effluvia  being  the  means  of  unition  ;  for  the  water  in 
humid  bodies  or  in  bodies  drenched  with  superficial  moisture 
on  the  top  of  water  has  the  force  of  an  effluvium.  A  clear 
atmosphere  is  a  good  medium  for  the  electric  effluvium  devel- 
oped from  concreted  humor.  Wet  bodies  projecting  out  of 
the  surface  of  water  come  together,  if  they  be  near,  and  unite. 


94 


WILLIAM  GILBERT. 


for  the  water's  surface  rises  around  wet  surfaces.  A  dry  body- 
does  not  move  toward  a  wet,  nor  a  wet  toward  a  dry,  but 
rather  they  seem  to  go  away  from  each  other ;  for  if  all  of  the 
body  that  is  above  the  water  is  dry,  the  nearest  water  surface 
does  not  rise  but  falls  away  with  subsidence  of  the  surface 
around  the  dry  object.  So,  too,  a  dry  body  does  not  run  to 
the  dry  rim  of  a  vessel  containing  water  ;  but,  on  the  contrary, 
a  wet  object  does.     In   the  figure,  AB  is  the  water  surface ; 


C,  D,  two  rods  with  their  projecting  ends  wet.  Evidently  the 
surface  of  the  water  at  C  and  D  rises  simultaneously  with  the 
rods ;  hence  the  rod  C,  because  its  water,  standing  above  the 
general  level,  seeks  equilibrium  and  union,  moves  with  the 
water  toward  D.  On  the  wet  rod  E  the  water  rises  also,  but 
by  the  dry  rod  F  the  water  is  depressed,  and  as  it  strives  to 
depress  also  the  water  rising  on  E,  the  higher  water  at  E 
turns  away  from  F,  for  it  refuses  to  be  depressed.  All  elec- 
tric attractions  are  effected  by  means  of  moisture,  and  thus 
all  things  come  together  because  of  humor :  fluid  bodies  and 
aqueous  bodies  come  together  on  the  surface  of  water,  and 
concreted  bodies,  if  reduced  to  vapor,  come  together  in  the 
air.  And  in  the  air  the  effluvium  of  electrics  is  very  rare,  that 
so  it  may  more  thoroughly  permeate  the  atmosphere,  and  yet 
not  give  it  impulsion  by  its  own  motion.  For  were  this  efiflu- 
vium  as  dense  as  air,  or  the  winds,  or  the  fumes  of  burning 


MAGNETIC  COITION.  95 

saltpetre,  or  as  the  thick,  foul  effluvia  emitted  with  much  force 
from  other  bodies,  or  as  the  air  from  vaporized  water  rushing 
forth  from  a  pipe  (as-  in  the  instrument  described  by  Hero  of 
Alexandria  in  his  book  Spiritualid) :  in  such  case  it  would 
repel  everything,  and  not  attract.  But  those  thinner  effluvia 
lay  hold  of  the  bodies  with  which  they  unite,  enfold  them,  as  it 
were,  in  their  arms,  and  bring  them  into  union  with  the  elec- 
trics ;  and  the  bodies  are  led  to  the  electric  source,  the  effluvia 
having  greater  force  the  nearer  they  are  to  that.  But  what  is 
the  effluvium  from  rock-crystal,  glass,  diamond — substances 
very  hard  and  very  highly  compressed  ?  For  such  effluvium 
there  is  no  need  of  any  notable  or  sensible  outflow  of  sub- 
stance :  no  need  of  abrading,  or  rubbing,  or  otherwise  dis- 
figuring the  electric  body:  odoriferous  substances  give  forth 
fragrance  for  many  years,  exhale  continually,  yet  are  not  soon 
consumed.  Cypress  wood,  as  long  as  it  remains  sound — and 
it  lasts  a  very  long  time — is  fragrant,  as  many  learned  men 
testify  from  experience.  Such  an  electric,  after  only  a  mo- 
ment's friction,  emits  powers  subtile  and  fine,  far  beyond  all 
odors ;  but  sometimes  an  odor  also  is  emitted  by  amber,  jet, 
sulphur,  these  bodies  being  more  readily  resolved.  Hence  it 
is  that  usually  they  attract  after  the  gentlest  friction,  or  even 
without  friction ;  and  they  attract  more  powerfully  and  keep 
hold  longer  because  their  effluvia  are  stronger  and  more  last- 
ing. But  diamond,  glass,  rock-crystal,  and  very  many  of  the  * 
harder  and  more  compacted  gems  are  heated,  and  then  rubbed 
for  a  good  while  at  first,  after  which  they,  too,  attract  strongly : 
they  cannot  be  resolved  in  any  other  way.  Electrics  attract 
all  things  save  flame  and  objects  aflame,  and  thinnest  air. 
And  as  they  do  not  draw  to  themselves  flame,  so  they  have 
no  effect  on  a  versorium  if  it  have  very  near  it  on  any  side  the 
flame  of  a  lamp  or  of  any  burning  substance  ;  for  it  is  plain 


96  WILLIAM  GILBERT, 

*that  the  effluvia  are  consumed  by  flame  and  igneous  heat. 
Therefore  electrics  do  not  attract  either  flame  or  bodies  near 
flame  ;  for  such  effluvia  have  the  virtue  and  analogy  of  rarefied 
humor,  and  they  will  produce  their  effect,  bringing  about 
unition  and  continuity,  not  through  the  external  action  of 
humors,  or  through  heat,  or  through  attenuation  of  heated 
bodies,  but  through  the  attenuation  of  the  humid  substance 

*  into  its  own  specific  effluvia.'  Yet  they  draw  to  themselves 
the  smoke  from  an  extinguished  candle  ;  and  the  lighter  the 
smoke  becomes  as  it  ascends,  the  less  strongly  is  it  attracted, 
for  substances  that  are  too  rare  do  not  suffer  attraction.     At 

*  last,  when  the  smoke  has  nearly  vanished,  it  is  not  attracted 
at  all,  as  is  plainly  seen  when  the  fact  is  observed  toward  the 
light.  But  when  it  has  passed  quite  into  the  air  it  is  not 
stirred  by  electrics,  as  has  already  been  shown.  For  thin  air 
itself  is  in  no  wise  attracted,  save  by  reason  of  its  coming  into 
a  vacuum,  as  is  seen  in  furnaces  in  which  air  is  supplied  by 
means  of  appliances  for  drawing  it  in.  Therefore  the  efflu- 
vium called  forth  by  a  friction  that  does  not  clog  the  surface 
— an  effluvium  not  altered  by  heat,  but  which  is  the  natural 
product  of  the  electric  body — causes  unition  and  cohesion, 
seizure  of  the  other  body,  and  its  confluence  to  the  electrical 
source,  provided  the  body  to  be  drawn  is  not  unsuitable  by 
reason  either  of  the  circumstances  of  the  bodies  or  of  its  own 
weight.  Hence  corpuscles  are  carried  to  the  electrical  bodies 
themselves.  The  effluvia  spread  in  all  directions :  they  are 
specific  and  peculiar,  and  sui  generis,  different  from  the  com- 
mon air ;  generated  from  humor ;  called  forth  by  calorific 
motion  and  rubbing,  and   attenuation  ;    they  are   as   it  were 

1  Nicolao   Cabeo,    Philosopkia  Magnetica,  1629,  Lib.  II,  Cap.  XXI,  page 
194. 


CONCERNING  MAGNETIC  COITION.  97 

material  rods — hold  and  take  up  straws,  chaff,  twigs,  till  their 
force  is  spent  or  vanishes ;  and  then  these  small  bodies,  being 
set  free  again,  are  attracted  by  the  earth  itself  and  fall  to  the 
ground.  The  difference  (distinction)  between  electric  and 
magnetic  bodies  is  this :  all  magnetic  bodies  come  together  by 
their  joint  forces  (mutual  strength) ;  electric  bodies  attract  the 
electric  only,  and  the  body  attracted  undergoes  no  modifica- 
tion through  its  own  native  force,  but  is  drawn  freely  under 
impulsion  in  the  ratio  of  its  matter  (composition).  Bodies  are* 
attracted  to  electrics  in  a  right  line  toward  the  centre  of  elec- 
tricity: a  loadstone  approaches  another  loadstone  on  a  line 
perpendicular  to  the  circumference  only  at  the  poles,  else- 
where obliquely  and  transversely,  and  adheres  at  the  same 
angles.  The  electric  motion  is  the  motion  of  coacervation  of 
matter  ;  the  magnetic  is  that  of  arrangement  and  order.  The 
matter  of  the  earth's  globe  is  brought  together  and  held  to- 
gether by  itself  electrically.  The  earth's  globe  is  directed  and 
revolves  magnetically  ;  it  both  coheres  and,  to  the  end  it  may 
be  solid,  is  in  its  interior  fast  joined/ 


CHAPTER  III. 

OPINIONS   OF   OTHERS   CONCERNING   MAGNETIC   COITION, 
WHICH   THEY   CALL  ATTRACTION. 

Having  treated  of  electrics,  we  have  now  to  set  forth 
the  causes  of  magnetic  coition.  Coition,  we  say,  not  attraction, 
for  the  term  attraction  has  wrongfully  crept   into   magnetic 


^  "In  these  obscure  axioms  we  trace  the  recognition  of  terrestrial  electric- 
ity'— the  expression  of  a  force, — which,  like  magnetism,  appertains  as  such  to 
matter.  As  yet  we  meet  with  no  allusions  to  repulsion,  or  the  difference 
between  insulators  and  conductors  "  (Humboldt,  "  Cosmos,"  1849,  Vol.  II.  page 
727). 


98  WILLIAM  GILBERT. 

philosophy,  through  the  ignorance  of  the  Ancients  ;  for  where 
attraction  exists,  there,  force  seems  to  be  brought  in  and  a 
tyrannical  violence  rules.  Hence,  if  we  have  at  any  time 
spoken  of  magnetic  attraction,  what  we  meant  was  magnetic 
coition  and  primary  confluence.'  But  here  it  will  be  not 
unprofitable  first  to  set  forth  briefly  the  views  of  others,  both 
among  the  ancients  and  the  moderns.  Orpheus,  in  his  hymns, 
tells  that  iron  is  drawn  by  the  loadstone  as  the  bride  to  the 
embraces  of  her  spouse.  Epicurus  holds  that  iron  is  drawn 
by  the  loadstone  as  straws  by  amber ;  and  adds  a  reason : 
"Atoms,"  he  says,  "and  indivisible  bodies  that  flow  from 
stone  and  from  iron,  agree  together  in  their  figures,  so  that 
they  readily  embrace  mutually  ;  hence,  when  they  impinge  on 
concretions  both  of  iron  and  stone,  they  rebound  into  the 
middle  space,  connected  together  on  the  way,  and  carry  the 
iron  with  them."  This,  surely,  cannot  be,  for  though  solid  and 
very  dense  bodies,  or  blocks  of  marble,  stand  between,  they 
do  not  hinder  the  passage  of  this  potency,  though  they  can 
separate  atoms  from  atoms ;  besides,  on  the  hypothesis,  the 
stone  and  iron  would  quickly  be  resolved  into  atoms,  so  pro- 
fuse and  incessant  would  be  the  atomic  outflow.  And  as  the 
mode  of  attraction  is  quite  different  in  amber,  there  the  Epicu- 
rean atoms  cannot  agree  in  their  figures.  Thales,  as  we  are 
told  by  Aristotle,  in  Book  I,  De  Anima,  deemed  the  loadstone 
endowed  with  a  sort  of  life,  because  it  possesses  the  power  of 
moving  and  attracting  iron.  Anaxagoras  was  of  the  same 
opinion.  The  opinion  of  Plato  in  the  Timcsus,  about  the 
effect  of  the  Herculean  stone,  is  baseless.  He  says:  "With 
respect  to  all  the  motions  of  water,  the  fallings  of  thunder,  and 


1  "  Coition,  says  Gilbert,  is  not  made  by  any  attractive  faculty,  either  of 
the  load-stone  or  of  the  iron,  but  by  a  Syndrome,  or  concordance  of  both  of 
them  "  (Creech's  translation  of  Lucretius,  London  1714,  Vol.  II,  page  720). 


CONCERNING  MAGNETIC  COITION.  99 

the  wonderful  circumstances  observed  in  the  attraction  of 
amber,  and  the  Herculean  stone, — in  all  these,  no  real  attrac- 
tion takes  place  at  all,  but,  as  a  vacuum  can  nowhere  be  found, 
the  particles  are  mutually  impelled  by  each  other;  hence,  as 
they  all  individually,  both  in  a  separate  and  mingled  state, 
have  an  attraction  for  their  own  proper  seats,  it  is  by  the 
mutual  intermingling  of  these  affections,  that  such  admirable 
effects  present  themselves  to  the  view  of  the  accurate  inves- 
tigator." '  Galen  knows  not  why  Plato  should  have  chosen 
rather  the  theory  of  circumpulsion  than  of  attraction  (on  this 
point  alone  differing  from  Hippocrates),  seeing  that  circumpul- 
sion harmonizes  in  fact  neither  with  reason  nor  with  experi- 
ment. For  neither  is  air  nor  anything  else  circumpelled,  and 
even  the  bodies  that  are  attracted  are  not  borne  to  the  attract- 
ing bo'v  in  confused  fashion  or  in  a  circle.  The  Epicurean 
poet  Lucretius  thus  presents  his  master's  theory  : 

Principio,  fluere  e  lapide  hoc  permulta  necesse  est 

Semina  sive  sestum,  qui  discutit  aera  plagis; 

Inter  qui  lapidem,  ferrumque  est,  cunque  locatus, 

Hoc  ubi  inanitur  spatium,  multisque  vacefit 

In  medio  locus  :  extemplo  primordia  ferri 

In  vacuum  prolapsa  cadunt  coniuncta  ;  fit  utque 

Annulus  ipse  sequatur,  eatque  ita  corpore  toto,  etc.^ 

*  In  his  note  to  the  translation  of  the  TimcBus  (Bohn,  London  1849, 
Vol.  II,  page  394),  Mr.  Henry  Davis  adds:  This  is  a  very  memorable 
passage,  and  clearly  shows  that  Plato  was  not  only  well  acquainted  with  the 
doctrine  of  attraction  and  repulsion,  but  was  of  opinion  also  that  the  law  of 
repulsion  depended  on  the  congregation  of  similar  elements  throughout  all  na- 
ture. The  whole  matter,  however,  is  largely  treated  by  Plutarch  in  his  Sixth 
Platonic  Dissertation,  Vol.  II,  page  1004,  ed.  Par. 

^  Mr  C.  F.  Johnson  renders  the  passage  as  follows  ("Nature  of  Things," 
1872,  page  291): 

First,  from  the  stone  innumerous  atoms  flow, 

In  streams  that  form  an  atmosphere  around. 

Displacing-  air  between  it  and  the  stone. 

Thus  rarefied,  the  space,  the  particles 

Of  metal  press,  vacated  place  to  fill, 

And  draff  with  them  the  mass  to  which  they're  joined  ; 

For  nothing-  is  than  steel  more  closely  knit, 


lOO  WILLIAM   GILBERT. 

A  similar  explication  is  offered  by  Plutarch  in  the  Qucss- 
tiones  PlatoniccE.  He  says  that  the  loadstone  emits  heavy 
exhalations,  whereby  the  contiguous  air,  being  impelled,  makes 
dense  the  air  in  front  of  it,  and  that  air,  driven  round  in  a 
circle  and  returning  to  the  part  whence  the  air  was  displaced, 
forcibly  carries  the  iron  with  it.  The  following  theory  of  the 
powers  of  loadstone  and  amber  is  propounded  by  Joannes 
Costaeus  of  Lodi :  Costaeus  holds  that  "there  is  work  on  both 
sides,  result  on  both  sides,  and  therefore  the  motion  is  pro- 
duced in  part  by  the  loadstone's  attraction,  in  part  by  the 
iron's  spontaneous  movement ;  for,  as  we  say  that  the  vapors 
given  out  by  the  loadstone  do  by  their  own  nature  haste  to 
attract  the  iron,  so,  too,  do  we  say  that  the  air  impelled  by 
the  vapors,  while  seeking  a  place  for  itself,  is  turned  back,  and 
when  turned  back  impels  and  transfers  the  iron,  which  is 
picked  up,  as  it  were,  by  it,  and  which,  besides,  is  exerted  on 
its  own  account.  In  this  way  there  is  found  a  certain  compos- 
ite movement,  resulting  from  the  attraction,  the  spontaneous 
motion,  and  the  impulsion ;  which  composite  motion,  how- 
ever, is  rightly  to  be  referred  to  attraction,  because  the  begin- 
ning of  this  motion  is  invariably  from  one  term,  and  its  end  is 
there  too  ;  and  that  is  precisely  the  distinguishing  character 
of  attraction."  There  is,  it  is  true,  mutual  action,  not  mutual 
work  ;  the  loadstone  does  not  thus  attract,  and  there  is  no  im- 
pulsion ;  neither  is  the  principle  of  the  motion  found  in  vapors 

Nor  more  compacted  in  its  elements  : 
Hence,  little  wonder,  if,  as  said  before, 
The  particles  thus  streaming  to  the  void 
Should  drag  with  them  along  the  chain  entire ! 
And  this  they  do  ;  drag  it  to  magnet  stone, 
Whereto  it  close  adheres  by  secret  bond. 
T.  LUCRETTI  Cari,  De  Reruni  Natura,  London  1824,  Book  VI,  v.  IOOO-1006. 

See  Thomas  Creech's  translation,  London  1714,  Vol.  II,  pages  726,  727; 
likewise  Mr.  H.  A.  J.  Monro's  Explanatory  Notes,  II,  Cambridge  and  London, 
1886,  pages  386,  387. 


CONCERNING  MAGNETIC  COITION.  lOI 

and  their  return  movements :  that  is  Epicurus's  theory,  so  oft 
repeated  by  others.  Galen  errs  in  his  first  book,  De  Naturali- 
bus  Faeultatibus,  cap.  14,  when  he  expresses  the  opinion  that 
whatever  agents  draw  out  the  venom  of  serpents  or  arrows 
possess  the  same  powers  as  the  loadstone.  As  for  this  attrac- 
tion (if  attraction  it  may  be  called)  of  medicaments,  we  will 
treat  of  it  in  another  place.  Drugs  against  poisons  and  arrow- 
wounds  have  no  relation,  no  resemblance,  to  the  actions  of 
magnetic  bodies.  Galen's  followers,  who  teach  that  purgative 
medicines  attract  because  of  likeness  of  substance,  say  that 
bodies  are  attracted  on  account  of  resemblance,  not  of  iden- 
tity ;  therefore,  say  they,  loadstone  draws  iron,  but  iron  does 
not  draw  loadstone.  But  we  say  and  prove  that  this  takes 
place  in  all  prime  bodies,  and  in  bodies  that  are  allied  and 
especially  that  are  near  akin  to  these,  and  this  on  account 
of  identity:  wherefore  loadstone  draws  loadstone,  and  iron 
draws  iron  ;  all  true  earth  substance  draws  its  kind  ;  and  iron 
invigorated  by  the  action  of  a  loadstone  within  whose  sphere 
of  influence  it  is,  draws  iron  more  powerfully  than  it  does 
loadstone.  Cardan  asks  why  no  other  metal  is  drawn  by  any 
stone  ;  and  his  answer  is,  because  no  other  metal  is  so  cold  as 
iron  :  as  if,  forsooth,  cold  were  cause  of  attraction,  or  iron  were 
much  colder  than  lead,  which  neither  follows  the  loadstone 
nor  leans  toward  it.  But  this  is  sorry  trifling,  no  better  than 
old  wives'  gossip.  Of  the  same  sort  is  the  beHef  that  the 
loadstone  is  a  living  thing,  and  that  iron  is  its  victual.  But 
how  does  loadstone  feed  on  iron  if  the  iron  filings  it  is  kept  in 
neither  are  consumed  nor  become  lighter  in  weight  ?  Corne- 
lius Gemma  {Cosmocrit,  X),  declares  that  loadstone  draws  iron 
to  itself  by  means  of  invisible  rods ;  and  to  this  opinion  he 
tacks  on  a  story  of  the  sucking-fish  and  the  catablepas.  Guil- 
elmus  Puteanus  deduces  the  power  of  the  loadstone,  not  from 


I02  WILLIAM   GILBERT. 

a  property  of  its  whole  substance  unknown  to  any  one  and  in- 
capable of  demonstration  (as  Galen  held,  and  after  him  nearty 
all  physicians),  but  from  ''  its  substantial  form  as  from  a  prime 
motor  and  self-motor,  and  as  from  its  own  most  potent  nature 
and  its  natural  temperament,  as  the  instrument  which  the 
efificient  form  of  its  substance,  or  the  second  cause,  which  is 
without  a  medium,  employs  in  its  operations.  So  the  load- 
stone attracts  iron  not  without  a  physical  cause,  and  for  the 
sake  of  some  good."  But  nothing  like  this  is  done  in  other 
bodies  by  any  substantial  form  unless  it  be  the  primary  one, 
and  this  Puteanus  does  not  recognize.  Naught  but  good  is 
assuredly  held  out  {sed  honiim  sane)  to  the  loadstone,  to  be  got 
from  the  appulsion  of  the  iron  (a  sort  of  friendly  association), 
yet  the  temperament  of  which  he  speaks  is  not  to  be  found, 
cannot  even  be  imagined  as  something  that  is  to  be  the  instru- 
ment of  the  form.  For  of  what  use  can  temperament  be  in 
magnetic  movements  that  are  calculable,  definite,  constant, 
comparable  to  the  movements  of  the  stars  ;  at  great  distance, 
with  thick,  dense  bodies  interposed.  In  Baptista  Porta's 
opinion,  the  loadstone  seems  to  be  a  mixture  of  stone  and 
iron,  i.e.,  ferruginous  stone,  or  stony  iron.  "  The  stone,"  he 
says,^  "is  not  changed  into  iron  so  as  to  lose  its  own  nature, 
nor  is  the  iron  so  merged  in  the  stone  but  that  it  retains  its 
own  essence  ;  and  while  each  strives  to  overcome  each,  from 
the  struggle  results  attraction  of  the  iron.  In  the  mass  (of  the 
loadstone)  there  is  more  stone  than  iron ;  therefore  the  iron, 
lest  it  should  be  dependent  on  (subdued  by)  the  stone,  craves 
the  strength  and  company  of  iron,  to  the  end  that  what  it 
cannot  procure  of  itself  it  may  obtain  by  the  help  of  the 
other.  .  .  .  The  loadstone  does  not  attract  stones  because  it 

»  "Natural  Magick,"  1658,  Book  VII,  Chap.  II. 


CONCERNING  MAGNETIC  COITION.  IO3 

has  no  need  of  them,  there  being  stone  enough  in  its  mass ; 
and  if  one  loadstone  attracts  another  that  is  not  for  the  sake 
of  the  stone,  but  of  the  iron  shut  up  in  the  stone."  As  though 
the  iron  in  a  loadstone  were  a  distinct  body  and  not  one 
blended  with  another,  like  all  other  metals  in  their  ores.  And 
it  is  height  of  absurdity  to  speak  of  these  substances,  thus 
confounded  together,  as  warring  with  each  other  and  quarrel- 
ing, and  calling  out  from  the  battle  for  forces  to  come  to  their 
aid.  Now,  iron  itself  when  touched  with  loadstone  seizes  iron 
with  not  less  force  than  loadstone  itself.  These  fights,  sedi- 
tions, conspiracies,  in  a  stone,  as  though  it  were  nursing  quar- 
rels as  an  occasion  for  calling  in  auxiliary  forces,  are  the 
maunderings  of  a  babbling  hag,  rather  than  the  devices  of  an 
accomplished  prestigiator.  Others  have  thought  that  the 
cause  is  a  sympathy.  But  even  were  fellow-feeling  there,  even 
so,  fellow-feeling  is  not  a  cause  ;  for  no  passion  can  rightly  be 
said  to  be  an  efficient  cause.  Others  again  assign  as  the  cause 
likeness  of  substance,  and  still  others  postulate  rods  {radii) 
imperceptible  to  the  senses.  These,  in  very  many  ways,  make 
a  sad  misuse  of  a  term  first  employed  by  mathematicians.  In 
more  scholarly  fashion,  Scaliger  declares  that  iron  moves  to  the 
loadstone  as  to  its  mother's  womb,  there  to  be  perfected  with 
recondite  principles,  as  the  earth  tends  to  the  centre.  The 
godlike  Thomas,'  in   Book  7  of  his  Pkysica,  treating  of  the 


*  Thomas  Aquinas,  famous  schoolman  of  the  middle  ages,  also  called  the 
Angelic  Doctor,  and  considered  by  many  the  greatest  of  Christian  philosophers, 
was  well  worthy  the  profound  respect  and  high  admiration  in  which  he  was 
held  by  our  author.  His  chief  work,  the  Summa  Theologice,  to  which  he  de- 
voted the  last  nine  years  of  his  life,  has  been  called  the  supreme  monument  of 
the  thirteenth  century.  One  of  his  biographers  remarks  that  those  wishing  to 
thoroughly  comprehend  the  peculiar  character  of  metaphysical  thought  in  the 
middle  ages  should  study  Aquinas,  in  whose  writings  it  is  seen  with  the 
greatest  consistency.  Aquinas  died  in  1274,  and  was  canonized  forty-nine 
years  later  by  Pope  John  XXII. 


I04  WILLIAM  GILBERT. 

causes  of  motion,  says  :  "  A  thing  can  in  another  sense  be  said 
to  pull,  in  that  it  moves  (an  object)  toward  itself,  by  altering 
it  in  any  way,  by  which  alteration  it  comes  about  that  the 
body  altered  moves  with  respect  to  place ;  and  in  this  way  is 
the  loadstone  said  to  draw  iron  :  for  as  a  generant  moves 
heavy  things  and  light  in  so  far  as  it  gives  them  the  form 
whereby  they  are  moved  to  a  place ;  so  does  the  loadstone 
give  to  iron  some  quality  through  which  it  is  moved  to  the 
loadstone."  This  view,  one  by  no  means  ill-conceived,  this 
most  learned  man,  proceeds  later  briefly  to  corroborate,  citing 
incredible  accounts  of  the  loadstone  and  of  the  power  of  garlic 
over  the  loadstone.  Nor  is  what  Cardinal  de  Cusa  states  to  be 
disregarded.  Says  he  :  "  Iron  hath  in  the  loadstone  a  certain 
principle  of  its  efflux,  and  while  the  loadstone  by  its  presence 
excites  the  heavy  and  ponderous  iron,  the  iron  is,  by  a  won- 
derful longing,  raised  above  the  natural  motion  (whereby  it 
ought  to  tend  downward  according  to  its  weight),  and  moves 
upward,  uniting  in  its  principle.  For  were  there  not  in  iron 
some  natural  foretaste  of  the  loadstone,  it  would  no  more 
move  toward  that  than  toward  any  other  stone ;  and  were 
there  not  in  the  loadstone  a  stronger  inclination  toward  iron 
than  toward  copper,  that  attraction  would  not  exist."  Such, 
as  propounded  by  different  writers,  are  current  opinions  about 
the  attraction  of  the  loadstone,  all  of  them  full  of  doubt  and 
uncertainty.  As  for  the  causes  of  magnetic  movements,  re- 
ferred to  in  the  schools  of  philosophers  to  the  four  elements 
and  to  prime  qualities,  these  we  leave  for  roaches  and  moths 
to  prey  upon. 


STRENGTH  OF  A   LOADSTONE.  IO5 


CHAPTER  IV. 

OF  THE  STRENGTH   OF    A  LOADSTONE    AND   ITS    FORM  :    THE 
CAUSE   OF   COITION. 

Quitting  the  opinions  of  others  about  the  attraction  of 
the  loadstone,  we  will  now  show  the  reason  of  its  coition  and 
the  nature  of  its  motion.  There  are  two  kinds  of  bodies  that 
are  seen  to  attract  bodies  by  motions  perceptible  to  our  senses 
— electric  bodies,  and  magnetic.  Electrical  bodies  do  this 
by  means  of  natural  efifluvia  from  humor ;  magnetic  bodies  by 
formal  efificiencies  or  rather  by  primary  native  strength  {vigor). 
This  form  is  unique  and  peculiar  :  it  is  not  what  the  Peri- 
patetics call  causa  formalis  and  causa  specifica  in  mixtis  and 
secunda  forma  ;  nor  is  it  causa  propagatrix  generantium.  corpo- 
rum;  but  it  is  the  form  of  the  prime  and  principal  globes  ;  and 
it  is  of  the  homogeneous  and  not  altered  parts  thereof,  the 
proper  entity  and  existence  which  we  may  call  the  primary, 
radical,  and  astral  form  ;  *  not  Aristotle's  prime  form,  but 
that  unique  form  which  keeps  and  orders  its  own  globe.  Such 
form  is  in  each  globe — the  sun,  the  moon,  the  stars — one  ;  in 
earth  also  'tis  one,  and  it  is  that  true  magnetic  potency  which 
we  call  the  primary  energy.  Hence  the  magnetic  nature  is 
proper  to  the  earth  and  is  implanted  in  all  its  real  parts 
according  to  a  primal  and  admirable  proportion.  It  is  not 
derived  from  the  heavens  as  a  whole,  neither  is  it  generated 
thereby  through  sympathy,  or  influence,  or  other  occult  quali- 
ties :  neither  is  it  derived  from  any  special  star  ;  for  there  is 
in  the  earth  a  magnetic  strength  or  energy  {vigor)  of  its  own, 

*  Whewell,  "  Hist,  of  Ind.  Sciences,"  1859,  Vol.  II,  Chap.  II,  page  220. 


I06  WILLIAM  GILBERT. 

as  sun  and  moon  have  each  its  own  forma ;  and  a  little  frag- 
ment of  the  moon  arranges  itself,  in  accordance  with  lunar 
laws  {lunatice),  so  as  to  conform  to  the  moon's  contour  and 
form,  or  a  fragment  of  the  sun  to  the  contour  and  form  of  the 
sun,  just  as  a  loadstone  does  to  the  earth  or  to  another  load- 
stone, tending'  naturally  toward  it  and  soliciting  it.  Thus  we 
have  to  treat  of  the  earth,  which  is  a  magnetic  body,  a  load- 
stone ;  then,  too,  of  its  true,  native  parts,  which  are  magnetic, 
and  of  how  they  are  affected  by  coition. 

A  body  that  is  attracted  by  a  magnetic  body  is  not  by  it 
altered,  but  remains  unimpaired  and  unchanged  as  it  was  be- 
fore, neither  has  it  now  greater  virtue.  A  loadstone  draws 
magnetic  bodies,  and  they  from  its  energy  eagerly  draw 
'  forces  not  in  their  extremities  only,  but  in  their  inmost  parts. 
For  an  iron  rod  held  in  the  hand  is  magnetized  in  the  end 
where  it  is  grasped,  and  the  magnetic  force  travels  to  the 
other  extremity,  not  along  the  surface  only,  but  through  the 
inside,  through  the  middle.  Electrical  bodies  have  material, 
corporeal  effluvia.  Is  any  magnetic  effluvium  emitted,  corpo- 
real or  incorporeal  ?  Or  is  nothing  at  all  that  subsists  emitted  ? 
But  if  the  effluvium  is  a  body,  it  must  needs  be  light  and  spir- 
itual so  as  to  enter  the  iron.  Is  it  such  as  is  exhaled  from 
lead  when  quicksilver,  which  is  liquid  and  fluid,  is  by  the  mere 
odor  and  vapor  of  lead  solidified,  and  remains  as  a  strongly 
coherent  metal  ?  Gold,  too,  which  is  very  solid  and  dense,  is 
reduced  to  a  powder  by  the  thin  vapor  of  lead.  Can  it  be 
that  as  quicksilver  can  enter  gold,  so  the  magnetic  odor  can 
enter  the  substance  of  iron,  changing  it  by  its  substantial 
property,  though  in  the  bodies  themselves  there  is  no  change 
perceptible  by  our  senses  ?  For  without  such  entering  a  body 
is  not  changed  by  another  body,  as  the  chemists,  not  without 
reason,  do  teach.     But  if   these   effects  were   produced   by  a 


STRENGTH  OF  A   LOADSTONE.  lO/ 

material  entrance,  then  were  resistant,  dense  bodies  interposed 
between  such  bodies  ;  or  were  the  magnetic  bodies  shut  up  in 
the  middle  of  very  thick,  dense  bodies,  objects  of  iron  would 
not  be  acted  on  by  the  loadstone.  Nevertheless,  these  two 
do  strive  to  come  together  and  are  changed.  Therefore  the 
magnetic  forces  have  no  such  conception,  no  such  origin,  as 
this :  nor  are  they  due  to  those  most  minute  particles  of  load- 
stone imagined  by  Baptista  Porta  concentrated  as  it  were 
into  hairs,  and  springing  from  friction  of  the  loadstone,  which 
parts  fastening  on  to  the  iron  give  it  the  magnetic  powers. 
For  the  electric  effluvia,  as  they  are  hindered  by  the  interposi- 
tion of  any  dense  body,  so  too  are  unable  to  attract  through  a 
flame,  or  if  a  flame  be  near  by.  But  iron,  which  is  hindered 
by  no  obstacle  (from)  deriving  from  the  loadstone  force  and 
motion,  passes  through  the  midst  of  a  flame  to  join  the  load- 
stone. Take  a  short  piece  of  iron  wire,  and  when  you  have* 
brought  it  near  to  a  loadstone  it  will  make  its  way  through 
the  flames  to  the  stone  ;  and  a  needle  turns  no  less  rapidly,  no 
less  eagerly,  to  the  loadstone  though  a  flame  intervenes  than 
if  only  air  stands  between.  Hence  a  flame  interposed  does 
not  prevent  coition.  But  were  the  iron  itself  red-hot,  it  cer- 
tainly would  not  be  attracted.  Apply  a  red-hot  iron  rod  to  a  * 
magnetized  needle  and  the  needle  stands  still,  not  turning  to 
the  iron ;  but  as  soon  as  the  temperature  has  fallen  somewhat 
it  at  once  turns  to  it.  A  piece  of  iron  that  has  been  magnet- 
ized, if  placed  in  a  hot  fire  until  it  becomes  red-hot,  and  per-«^ 
mitted  to  remain  for  a  little  while,  loses  the  magnetic  power.' 

^  "  For  if  a  Load-stone  be  made  red  hot,  it  loseth  the  magnetical  vigour  it 
had  before  in  itself,  and  acquires  another  from  the  Earth  in  its  refrigeration; 
for  that  part  which  cooleth  toward  the  Earth  will  acquire  the  respect  of  the 
North,  and  attract  the  Southern  point  or  cuspis  of  the  Needle"  (Thomas 
Brown,  Pseudoloxia  Epidemica,  1658,  page  65).  Kenelm  Digby,  "  The  Nature  of 
Bodies,"  1645,  Chapter  XXI,  pages  232-233. 


I08  WILLIAM  GILBERT. 

Even  loadstone  itself  loses  its  native  and  inborn  powers  of  at- 
tracting, and  all  other  magnetic  properties,  if  left  long  in  fire. 
And  though  some  magnetic  ores  when  roasted  exhale  a  deep- 
blue  or  sulphurous  and  foul-smelling  vapor,  nevertheless  such 
vapor  is  not  the  soul  of  the  loadstone ;  neither  is  it  the  cause 
of  the  attraction  of  iron,  as  Porta  supposes.*  Nor  do  all 
loadstones  when  roasted  or  burned  smell  of  sulphur  or  give 
out  sulphur  fumes  :  that  property  is  something  added,  a  sort 
of  congenital  evil  which  comes  from  the  foul  bed  or  matrix 
in  which  the  loadstone  is  produced ;  nor  does  the  material 
corporeal  cause  introduce  into  the  iron  anything  of  the  same 
sort,  for  iron  derives  from  loadstone  the  power  of  attracting 
and  the  property  of  verticity,  though  glass  or  gold  or  another 
sort  of  stone  stand  between,  as  later,  when  treating  of  the 
magnetic  direction,  we  shall  clearly  prove.  But  fire  destroys 
in  the  loadstone  the  magnetic  qualities,  not  because  it  plucks 
out  of  it  any  particular  attractional  particles,  but  because  the 
quick,  penetrating  force  of  the  flame  deforms  it  by  breaking 
its  matter  up ;  just  as  in  the  human  body  the  soul's  primary 
powers  are  not  burnt,  though  yet  the  burnt  body  remains 
without  faculties.  But  though  the  iron  remains  after  perfect 
ignition,  and  is  not  converted  into  either  ash  or  slag ;  still,  as 
Cardan  not  injudiciously  remarks,  red-hot  iron  is  not  iron,  but 
something  lying  outside  its  own  nature,  until  it  returns  to 
itself.  For  just  as,  by  the  cold  of  the  ambient  air,  water  is 
changed  from  its  own  nature  into  ice,  so  iron  made  white-hot 
by  fire  has  a  confused,  disordered  form,  and  therefore  is  not 
attracted  by  a  loadstone,  and  even  loses  its  power  of  attract- 
ing, however  acquired ;  it  also  acquires  a  different  verticity 
when,  as  though  born  anew,  it  is  impregnated  by  a  loadstone 


»  Porta's  "  Natural  Magick,"  1658,  Book  VII,  Chapter  II. 


STRENGTH  OF  A   LOADSTONE.  IO9 

or  the  earth ;  in  other  words,  when  its  form,  not  utterly  de- 
stroyed, yet  confused,  is  restored.  I  shall  have  more  to  say 
on  this  subject  when  treating  of  changed  verticity  (Book  III, 
Chap.  10).  Hence,  Fracastorio  finds  no  confirmation  of  his 
opinion  that  the  iron  is  not  altered;  "for,"  says  he,  "if  it 
were  altered  by  the  loadstone's  form,  the  form  of  the  iron 
would  be  spoiled."  Yet  this  alteration  is  not  generation,  but 
restitution  and  re-formation  of  a  confused  form. 

Hence  that  is  not  corporeal  which  emanates  from  the  load- 
stone, or  which  enters  the  iron,  or  which  is  given  forth  again 
by  the  awakened  iron ;  but  one  loadstone  gives  portion  to 
another  loadstone  by  its  primary  form.  And  a  loadstone  re- 
calls the  cognate  substance,  iron,  to  formate  energy  and  gives 
it  position :  hence  does  it  leap  to  the  loadstone  and  eagerly 
conforms  thereto  (the  forces  of  both  harmoniously  working  to 
bring  them  together) ;  for  the  coition  is  not  indeterminate  and 
confused,  it  is  not  a  violent  inclination  of  body  to  body,  not  a 
mad  chance  confluence.  Here  no  violence  is  offered  to  bodies, 
there  are  no  strifes  or  discords ;  but  here  we  have,  as  the  con- 
dition of  the  world  holding  together,  a  concerted  action, — to 
wit,  an  accordance  of  the  perfect,  homogeneous  parts  of  the 
world's  globes  with  the  whole,  a  mutual  agreement  of  the  chief 
forces  therein  for  soundness,  continuity,  position,  direction, 
and  unity.  In  view  of  this  so  wonderful  effect,  this  stupendous 
innate  energy, — an  energy  (strength)  not  existing  in  other 
elements, — the  opinion  of  Thales  the  Milesian  is,  in  Scaliger's 
judgment,  not  utterly  absurd,  not  a  lunatic's  fancy.  Thales 
ascribed  to  the  loadstone  a  soul,  for  it  is  incited,  directed,  and 
moved  in  a  circle  by  a  force  that  is  entire  in  the  whole  and 
entire  in  each  part,  as  later  will  appear,  and  because  it  seems 
most  nearly  to  resemble  a  soul.  For  the  power  of  self-move- 
ment seems  to  betoken  a  soul,  and  the  supernal  bodies,  which 


no  WILLIAM  GILBERT. 

we  call  celestial,  as  it  were  divine,  are  by  some  regarded  as 
animated  because  that  they  move  with  wondrous  regularity. 
If  two  loadstones  be  set  over  against  each  other  in  their  floats 
on  the  surface  of  water,  they  do  not  come  together  forthwith, 
but  first  they  wheel  round,  or  the  smaller  obeys  the  larger  and 
takes  a  sort  of  circular  motion ;  at  length,  when  they  are  in 
their  natural  position  they  come  together.  In  iron  that  has 
not  been  excited  by  the  loadstone,  there  is  no  need  of  these 
preliminaries  ;  for  iron,  though  made  from  the  finest  loadstone, 
has  no  verticity  save  such  as  it  gets  by  chance  and  momen- 
tarily ;  and  this  is  not  stable  nor  fixed,  for  while  it  ran  liquid  in 
the  furnace  its  parts  were  thrown  into  confusion.  Such  a  body 
instantly  receives  from  the  presence  of  the  loadstone  verticity 
and  natural  conformity  to  it,  being  powerfully  altered  and 
converted,  and  absolutely  metamorphosed  into  a  perfect  mag- 
net :  so,  like  an  actual  part  of  the  loadstone,  it  flies  to  it.  For 
there  is  naught  that  the  best  loadstone  can  do  which  cannot 
be  done  by  iron  excited  by  a  loadstone — not  magnetized  at 
all,  but  only  placed  in  the  neighborhood  of  a  loadstone.  For 
as  soon  as  it  comes  within  the  loadstone's  sphere  of  influence, 
though  it  be  at  some  distance  from  the  loadstone  itself,  the 
iron  changes  instantly,  and  has  its  form  renewed,  which  before 
was  dormant  and  inert,  but  now  is  quick  and  active :  all  this 
will  appear  clearly  when  we  come  to  present  the  proofs  of 
magnetic  direction  (in  Book  III).  Thus  the  magnetic  coition 
is  the  act  of  the  loadstone  and  of  the  iron,  not  of  one  of  them 
alone :  it  is  evrekexeioc,  not  epyov-  it  is  (Tvvevrekexeia  and 
conactus  (mutual  action)  rather  than  sympathy.  There  is, 
properly  speaking,  no  magnetic  antipathy ;  for  the  flight  and 
turning  away  of  the  poles  and  the  wheeling  around  of  the 
whole  is  the  act  of  each  of  the  two  toward  unition,  resulting 


STRENGTH  OF  A   LOADSTONE.  1 1 1 

from  the  <Tvvevrekex^'iOL  and  conactus^  of  both.     Thus   the 
iron  puts  on  anew  its  form  ;  and  because  that  is  awakened,  as 
also  in  order  more  surely  to  gain  its  form,  it  rushes  headlong 
on  the  loadstone,  and  not  with  circlings  and  wheehngs,  as  in 
the  case  of  two  loadstones.     For  as,  long  ages  ago,  nay  at  the 
very  beginning  of  things,  there  were  gendered  in  the  loadstone 
and   therein  fixed  verticity  and  the  power  of  coordinating ; 
and  since  the  great  mastering  form  of  the  earthly  globe  can- 
not be  readily  changed  by  another  magnet,  as  iron  is  changed, 
therefore,  the  nature  of  each  being  constant,  neither  hath  the 
momentary  power  of  altering  the  verticity  of  the  other,  but 
the  two  do  but  come  to  agreement  with  each  other.     And 
magnetized  iron,  in  case  it  is  unable  for  whatever  reason  to  # 
cause  the  piece  of  iron  in  the  natural  state  to  turn,  as  does  the 
pointer  of  a  versorium,  is  itself  seized  at  either  end  by  a  load- 
stone brought  nigh  it.     For  the  loadstone,  as  it  imparts  so  can  it 
alter  verticity,  and  it  can  in  an  instant  bestow  the  formal  energy 
in  either  end.     Thus  iron  may  be  transformed  variously,  as 
that  form  is  adventitious  and  has  not  yet  abided  long  in  the 
metal.     In  iron,  because  its  body  is  fused  when  a  magnetic  or 
a  ferruginous  ore  is  smelted,  the  virtue  of  the  primal  form, 
which   previously   existed    distinct,  is    now  confused ;   but   a 
sound  loadstone,  when  brought  near,  sets  up  again  the  primal 
action :   the   form,    now   arranged    and    ordered    again,   joins 
forces  with  the  loadstone,  and,  each  with  other,  the  two  come 
to  agreement,  after  the  manner  of  the  loadstone,  in  all  their 
movements  toward  union  ;  they  enter  into  alliance,  and  whether 
joined  by  bodily  contact  or  standing  within  their  sphere  of 
influence,  are  one  and  the  same.     For  when  iron  is  reduced  in 
the  furnace  from  its  ore,  or  when  steel  is  got  from  its  ore, 


'  Conactus,  i.e.,  combined  or  mutual  action.     See  Book  V,  Chapter  XII. 


112  WILLIAM  GILBERT. 

which  is  loadstone,  the  metallic  matter  is  melted  and  becomes 
fluid,  and  the  iron  and  the  steel  run  off,  leaving  their  slag  :  this 
slag  consists  of  matter  spoilt  by  the  intense  heat  of  the  fire, 
or  of  useless  matter,  or  of  dross,  due  to  some  imperfection  or 
to  some  intermixture  in  the  projecting  surface  of  the  earth. 
Thus  the  iron  or  steel  is  a  purified  material,  wherein  the  metal- 
lic element,  all  disordered  by  the  smelting  (for  the  forces  of 
that  primal  form  are  all  confused  and  unsettled),  is  brought 
back  again,  as  it  were,  to  life,  to  normal  form,  and  to  complete- 
ness. Its  matter  is  thus  awakened,  and  tends  to  union,  which 
is  the  bond  of  the  universe  and  the  necessary  condition  of  the 
conservation  of  all  things. 

For  this  reason,  and  because  of  the  purging  of  the  ore  and 
its  change  into  a  purer  body,  the  loadstone  gives  to  iron 
greater  power  of  attracting  than  exists  in  itself.  For  if  you 
♦  put  some  iron-filings  or  a  nail  on  a  large  magnet,  a  piece  of 
iron  joined  to  the  magnet  steals  the  filings  and  the  nail,  and 
holds  them  as  long  as  it  remains  alongside  the  magnet :  so, 
too,  iron  attracts  iron  more  powerfully  than  does  a  loadstone, 
if  the  iron  be  afformed,  and  remain  within  the  sphere  of  the 
form  given  out  to  it.  Again,  a  piece  of  iron  nicely  adjusted 
to  the  pole  of  a  loadstone  holds  a  greater  weight  than  the 
loadstone  does.  So,  then,  iron  and  steel  are  the  better  ele- 
ments of  their  ores,  purified  by  the  action  of  fire,  and  the  load- 
stone impregnates  them  again  with  their  forms ;  wherefore  to 
it  do  they  come  by  spontaneous  approach,  so  soon  as  they 
enter  the  circle  of  the  magnetic  forces,  for  by  it  are  they  first 
possessed,  and  made  continuous,  and  united  with  perfect  union. 
Once  within  that  circle  they  have  absolute  continuity,  and  they 
are  joined  by  reason  of  their  accordance,  albeit  the  bodies 
themselves  be  separated.  For  the  iron  is  not,  after  the  man- 
ner of  electrics,  possessed  and  pulled  by  substantial  effluvia, 


STRENGTH  OF  A  LOADSTONE.  II3 

but  only  by  the  immaterial  act  of  the  form  or  by  its  incorporeal 
going  forth,  which  as  in  a  continuous  and  homogeneous  body 
doth  act  in  the  iron  subjectum,  and  is  received  into  it ;  nor 
has  it  need  of  wider  paths. 

Hence  it  is  that,  with  the  densest  bodies  interposed,  the 
iron  is  put  in  motion  throughout  and  is  attracted,  and  that  the 
iron,  in  presence  of  the  loadstone  thoroughly  stirs  and  attracts 
the  loadstone  itself,  and  that  with  their  mutual  forces  they 
make  that  rush  toward  union  which  commonly  is  called  attrac- 
tion. But  these  formal  forces  sally  forth  and  in  meeting  unite ; 
and  the  force  conceived  in  the  iron,  that  also  forthwith  has  its 
efiflux.  But  Julius  Scaliger,  who,  in  his  344th  disquisition, 
cites  other  examples  to  prove  this  explanation  to  be  absurd,  is 
far  astray.  For  the  virtues  of  prime  bodies  are  not  compara- 
ble with  those  that  are  derivate  and  mixed.  Were  he  still 
among  the  living,  he  might  now,  in  the  chapter  on  Effused 
Magnetic  Spherical  Forms,  discover  what  is  the  nature  of 
effused  forms. 

But  if  iron  be  badly  injured  by  rust  it  is  but  little  or  not  at 
all  affected  by  the  loadstone,  for  when  the  metal  is  corroded 
and  marred  by  external  causes  or  by  decay  it  is  spoilt,  as  has 
been  said  of  the  loadstone,  and  loses  its  prime  qualities  that 
are  conjoined  to  its  form,  or,  the  stone  being  impaired  by  age, 
these  qualities  are  weak  and  feeble ;  neither  can  it  be  duly  in- 
formed when  once  it  has  suffered  decay.  But  a  strong,  fresh 
{vegetus)  loadstone  pulls  all  sound  clean  iron,  and  the  iron 
(having  conceived  force)  powerfully  attracts  other  iron — as 
pieces  of  iron  wire,  iron  nails ;  and  not  only  these  separately 
and  directly,  but  one  after  another,  one  at  the  end  of  another, 
thus  holding  three,  four,  or  five:  thus  forming  as  it  were  a 
chain,  the  successive  nails  sticking  to  one  another  and  sus- 
pended  from   one   another.      But   the   loadstone  would   not 


114  WILLIAM  GILBERT. 

attract  the  last  piece  in  such  a  line  if  there  were  no  nails  in 
the  mid-space.  Thus  a  loadstone  placed  at  A  pulls  the  nail 
or  bar  B,  and,  in  like  manner,  after  B  pulls  C,  and  after  C,  D ; 
but  at  the  same  distance  does  not  pull  aloft  D\  that  is  so  for 

If  C  s 

^liinillimilllliHilililllilfllllllllH  ,milllilliliill.miHllllllltllMHla  iii.iriiMiiiiimiuimimmminni 

the  reason  that  when  the  nails  form  an  unbroken  line  the 
presence  of  the  loadstone  A,  because  of  its  proper  forces, 
raises  the  magnetic  form  of  the  iron  objects  B  and  C,  and 
makes  them  as  it  were  its  auxiliary  forces,  while  B  and  C,  like 
a  continuous  magnetic  body,  conduct  on  to  D  the  force  where- 
by it  is  seized  or  conformed,  yet  not  so  powerfully  as  C  is 
seized  by  B.  And  these  iron  nails  derive  the  force  from  the 
mere  contact,  and  from  the  presence  of  the  loadstone  without 
contact,  and  they  retain  it  in  their  bodies,  as  will  be  shown 
when  we  treat  of  Direction  (Book  III).  For  the  iron  does  not 
assume  these  powers  only  while  in  presence  of  a  loadstone,  nor 
does  it  hold  them  of  the  stone  only  momentarily  as  [the  distin- 
guished orator  "  Euphrades "]  Themistius  [of  Paphlagonia] 
supposes  in  his  Physica,  VIII.  The  best  iron  (steel)  is  solicited 
by  the  loadstone  from  a  greater  distance,  a  greater  weight  of 
it  is  lifted,  it  is  more  powerfully  held,  and  it  acquires  greater 
force,  than  does  common,  cheaper  iron,  for  it  is  made  of  the 
best  ore  or  of  loadstone,  and  is  imbued  with  superior  forces  ; 
but  iron  from  impure  ores  is  weaker,  and  is  attracted  more 
feebly.  As  for  what  Fracastorio  writes,  of  having  seen  a  bit 
of  loadstone  that  on  one  side  attracted  loadstone  but  not  iron, 
on  another  side  attracted  iron  but  not  loadstone,  and  on 
another  attracted  both, — proof,  according  to  him,  that  in  one 
spot  there  was  more  loadstone,  in  another  more  iron,  in  the 
third  the  two  were  present  equally ;  hence  the  difference  in 


IN   WHAT  MANNER  ENERGY  INHERES.  II5 

the  attraction, — all  this  is  utterly  erroneous,  and  the  result  of 
mal-observation  on  the  part  of  Fracastorio,  who  did  not  know 
how  to  present  one  loadstone  to  another  properly.  Loadstone 
attracts  iron  and  loadstone  if  both  be  properly  situated,  and 
free  to  move  and  unrestrained.  A  light  object  is  more  readily 
moved  from  its  position  and  place  than  a  heavy  one,  for  heavy 
objects  make  greater  resistance,  but  a  light  object  bestirs 
itself  to  meet  a  heavy  one  and  is  pulled  by  it. 


CHAPTER  V. 

IN  WHAT  MANNER  THE  ENERGY  INHERES  IN  THE   LOADSTONE. 

That  the  loadstone  draws  loadstone,  iron,  and  other  mag- 
netic bodies  was  shown  in  Book  I,  as  also  by  what   forces  the 
magnetic  coition  is  regulated  ;  we  have  now  to  inquire  how 
this  energy  is  ordered   in   magnetic   bodies.     Here  we  must 
bring  in  the  analogy  of  a  large  loadstone.     A  magnetic  body 
unites  forcibly  with  a  loadstone  if  the  loadstone  is  powerful, — 
\ -eebly  if  it  be  defective  or  if  it  has  from  any  fault  become  im 
paired.     Loadstone  does  not  attract  iron  with  equal  force  at 
every  point ;  in  other  words,  the  magnetic  body  does  not  tend 
with  the  same  force  to  every  point  of  the  loadstone ;  for  the 
loadstone  has  points  (i.e.,  true  poles)  at  which  its  rare  energy 
is  most  conspicuous.     And  the  regions  nearest  the  poles  are 
the  stronger,  those  remotest  are  the  weaker ;   yet  in  all  the 
energy  is  in  some  sense  equal.     In  the  figure  of  a  terrella, 
A,  B,  are  the  poles,  CD  is  the  equinoctial  line ;    the  greatest 
attractive  force  is  seen  at  A  and  B.     At  C  and  Z*  there  is  no 
force  that  attracts  to  the  body  the  ends  of  magnetic  objects, 


ii6 


WILLIAM  GILBERT, 


for  the  forces  tend  toward  each  of  the  poles.  But  the  directive 
force  at  the  equator  is  strong.  C  and  D  are  at  equal  distances 
from  both  poles ;  hence  a  piece  of  iron  on  the  line  CD,  being 


pulled  in  contrary  directions,  does  not  cling  steadily,  but  it 
stays  and  adheres  to  the  stone  only  when  it  falls  to  either  side 
of  the  line.  At  E  the  attractive  force  is  greater  that  at  F,  for 
E  is  nigher  the  pole.  And  this  is  not  for  the  reason  that  there 
is  more  energy  resident  at  the  pole,  but  because  all  the  parts, 
being  united  in  the  whole,  direct  their  forces  to  the  pole. 

By  the  confluence  of  the  forces  from  the  plane  of  the 
equinoctial  toward  the  pole  the  energy  increases  poleward, 
*and  absolute  verticity  is  seen  at  the  pole  so  long  as  the  load- 
stone remains  whole ;  but  let  it  be  divided  or  broken  up,  and 
in  the  separate  parts  the  verticity  will  find  other  abiding- 
places.  For  with  change  of  mass  always  goes  change  of  ver- 
ticity. Hence,  if  the  terrella  be  severed  along  the  line  AB  so 
as  to  make  two  stones,  the  poles  in  the  severed  parts  will  not 
be  AB,  but  FG  and  HI.  And  though  these  two  stones  now 
are  so  interrelated  that  F  does  not  tend  to  H,  nevertheless  if, 
before  division,  A  was  the  north  pole,  F  likewise  is  now  north, 
as  is  H  also.     For  the  verticity  is  not  reversed,  as  Baptista 


IN   WHAT  MANNER  ENERGY  INHERES. 


117 


Porta  erroneously  affirms  (Porta,  VII,  4) ;'  for  though/^  and 
H  are  not  so  related  as  mutually  to  attract,  yet  the  two  turn 
to  the  same  point  of  the  horizon.  If  the  hemisphere  HI  be 
cut  in  two  quarter  spheres,  one  pole  will  be  at  H  and  the 
other  at  /.     The  integral  mass  of  the  stone,  as  I  have  said, 


^     A    TI 


gives  to  the  vertex  or  pole  a  constant  place  ;  and  any  part  of 
the  stone,  before  it  was  hewed  out  of  the  rock  might  have 
been  the  pole  or  vertex:  but  of  this  we  shall  have  more  to  say 
under  Direction.  For  the  present,  the  thing  to  be  understood 
and  to  be  borne  steadily  in  mind  is,  that  the  poles  are  domi- 
nant in  virtue  of  the  force  of  the  whole,  for  (the  magnetic 
empire  being  divided  in  two  by  the  equinoctial  line)  all  the 


1  John  Baptist  Porta,  "Natural  Magick,"  1658,  Book  VII,  Chapter  IV, 
page  193:  "But  the  two  points  we  speak  of  are  the  end  of  the  right  line,  run- 
ning through  the  middle  of  the  stone  from  North  to  south;  if  any  man  break 
the  stone,  and  break  this  line,  those  ends  of  the  division  will  presently  be  of 
another  property  and  vertue,  and  will  be  enemies  one  to  the  other:  which  is 
great  wonder:  for  these  two  points,  when  they  were  joined  together,  had  the 
same  force  of  turning  to  the  pole,  but,  now  being  parted  asunder,  one  will  turn 
to  the  North,  the  other  to  the  South,  keeping  the  same  posture  and  position 
they  had  in  the  Mine  where  they  were  bred:  and  the  same  happens  in  the  least 
bits  that  are  seen  in  the  greatest  load-stone." 


u8 


WILLIAM  GILBERT. 


forces  of  the  hemisphere  tend  north,  and,  conversely,  all  those 
of  the  other  hemisphere  tend  south,  so  long  as  the  parts  are 
united,  as   appears  from  the  following    demonstration.      For 


the  whole  force  tends  separately  to  the  two  poles  along  an 
infinity  of  curves  starting  from  every  point  of  the  equator  that 
divides  the  sphere  into  two  equal  parts :  from  every  point 
of  the  superficies  from  the  equator  to  the  north  on  one  side, 
and  from  the  equator  to  the  south  on  the  other.  Hence  the 
verticity  is,  in  each  hemisphere,  from  the  equinoctial  circle  to 
the  pole.  This  force  resides  in  the  whole  mass.  From  A  the 
energy  is  transmitted  to  B,  from  AB  to  C,  from  ABC  to  D, 
and  from  them  to  E,  and  likewise  from  GtoH;  and  so  on  as 
long  as  the  whole  mass  is  one  body.     But  if  the  piece  AB  be 


IN    WHAT  MANNER  ENERGY  INHERES.  1 19 

cut  out,  though  it  be  near  the  equator,  nevertheless  the  effect 
will  be  as  great  on  the  magnetic  action  as  if  CD  or  DE,  equal 
quantities,  had  been  taken  away.  For  no  part  has  any  super- 
eminent  value  in  the  whole  ;  whatever  it  be,  that  it  is  because 
of  the  parts  adjoining,  whereby  an  absolute  and  perfect  whole 
is  produced. 

DIAGRAM  OF  THE  MAGNETIC  ENERGY  DIFFUSED  FROM  THE 
PLANE  OF  THE  EQUATOR  TO  THE  PERIPHERY  OF  A  TER- 
RELLA  OR  OF  THE  EARTH. 

Let  HEQ  be  a  terrella,  E  a  pole,  M  the  centre,  HMQ  the 
plane  of  the  equinoctial  circle.  From  every  point  of  the 
equinoctial  plane  the  energy  reaches  out  to  the  periphery,  but 
differently  from  each  :  for  from  A  the  formal  energy  goes 
toward  CFNE  and  to  every  point  betwixt  C  and  E  (the  pole), 
and  not  toward  B ;  neither  from  G  toward  C.  The  attractive 
force  in  the  region  FGH  is  not  strengthened  by  the  force 
residing  in  the  region  GMFE  ;  but  FGH  increases  the  energy 
in  the  rising  curve  FE.  Thus  energy  never  proceeds  from  the 
lines  parallel  to  the  axis  to  points  above  those  parallels,  but 
always  internally  from  the  parallels  to  the  pole.  From  every 
point  of  the  plane  of  the  equator  the  energy  goes  to  the 
pole  E  ;  the  point  F  derives  its  forces  only  from  GH,  and  the 
point  N  from  OH;  but  the  pole  E  is  strengthened  by  the 
whole  plane  HO.  Therefore  this  mighty  power  has  here  its 
chief  excellency;  here  is  its  throne,  so  to  speak.  But  in  the 
intervals  at  F,  for  example,  there  resides  so  much  attractional 
energy  as  can  be  given  by  the  section  HG  of  the  plane. 


120 


WILLIAM  GILBERT. 


MAGNETIZED  IRON  AND  SMALLER  LOADSTONES.     121 


CHAPTER  VI. 

HOW  MAGNETIZED  IRON  AND  SMALLER  LOADSTONES  CON- 
FORM TO  THE  TERRELLA  AND  TO  THE  EARTH  ITSELF, 
AND   ARE   GOVERNED   THEREBY. 

Coition  of  bodies  that  are  separate  from  one  another,  and 
that  cohere  naturally,  takes  place  by  another  sort  of  move- 
ment, if  they  be  free  to  move.  The  terrella  sends  its  force 
abroad  in  all  directions,  according  to  its  energy  and  its  quality. 
But  whenever  iron  or  other  magnetic  body  of  suitable  size 
happens  within  its  sphere  of  influence  it  is  attracted  ;  yet  the 
nearer  it  is  to  the  loadstone  the  greater  the  force  with  which 
it  is  borne  toward  it.  Such  bodies  tend  to  the  loadstone  not  * 
as  toward  a  centre  nor  towards  its  centre :  that  they  do  only 
at  its  poles,  i.e.,  when  that  which  is  attracted  and  the  pole  of 
the  loadstone,  as  well  as  its  centre,  are  in  a  right  line.  But  in 
the  intervals  between  they  tend  to  it  in  an  oblique  line,  as 
seen  in  the  figure  below,  wherein  is  shown  how  the  force  goes 
out  to  the  magnetic  associate  bodies  within  the  sphere.  At 
the  poles  the  line  is  a  right  one.  The  nearer  the  parts  to 
the  equinoctial  circle  the  more  obliquely  do  magnetic  bodies 
attract,  but  the  parts  nearer  the  poles  attract  more  directly ; 
at  the  poles  themselves  attraction  is  in  a  right  line.  All  load- 
stones alike,  whether  spherical  or  oblong,  have  the  self-same 
mode  of  turning  to  the  poles  of  the  world  ;  but  it  is  easiest  to 
experiment  with  oblong  ones.  For  whatever  the  shape,  ver- 
ticity  is  present,  and  there  are  poles ;  but  owing  to  imperfect 
and  irregular  shape,  loadstones  are  often  subject  to  drawbacks, 


122  WILLIAM  GILBERT. 

and  are  interfered  with  in  their  movements.     If  the  loadstone 
be  oblong,  with  vertices  at  the  extremities   and  not    at  the 


sides,  it  attracts  best  at  the  vertex ;  for  the  parts  convey  to 
the  poles  a  greater  force  in  right  lines  than  in  oblique.  Thus 
do  the  loadstone  and  the  earth  conform  magnetic  movements. 


POTENCY  OF   THE  MAGNETIC  FORCE.  1 23 


CHAPTER   VII. 

OF    THE   POTENCY    OF    THE    MAGNETIC    FORCE,   AND    OF    ITS 
SPHERICAL    EXTENSION.' 

The  magnetic  force  is  given  out  in  all  directions  around 
the  body ;  around  the  terrella  it  is  given  out  spherically ; 
around  loadstones  of  other  shapes  unevenly  and  less  regularly. 
But  the  sphere  of  influence  does  not  persist,  nor  is  the  force 
that  is  diffused  through  the  air  permanent  or  essential ;  the 
loadstone  simply  excites  magnetic  bodies  situate  at  convenient 
distance.  And  as  light — so  opticians  tell  us — arrives  instantly 
in  the  same  way,  with  far  greater  instantaneousness,  the  mag- 
netic energy  is  present  within  the  limits  of  its  forces ;  and 
because  its  act  is  far  more  subtile  than  light,  and  it  does  not 
accord  with  non-magnetic  bodies,  it  has  no  relations  with  air, 
water,  or  other  non-magnetic  body ;  neither  does  it  act  on 
magnetic  bodies  by  means  of  forces  that  rush  upon  them  with 
any  motion  whatever,  but  being  present  solicits  bodies  that 
are  in  amicable  relations  to  itself.  And  as  a  light  impinges 
on  whatever  confronts  it,  so  does  the  loadstone  impinge  upon 
a  magnetic  body  and  excites  it.  And  as  light  does  not  remain 
in  the  atmosphere  above  the  vapors  and  effluvia  nor  is  re- 
flected back  by  those  spaces,  so  the  magnetic  ray  is  caught 
neither  in  air  nor  in  water.  The  forms  of  things  are  in  an 
instant  taken  in  by  the  eye  or  by  glasses ;  so  does  the  mag- 
netic force  seize   magnetic  bodies.     In  the  absence  of  light 


1  Sir  Kenelm  Digby,  "A  Treatise  of  Bodies,"  London  1645,  Chap.   XXI, 
pages  238,  239. 


124 


WILLIAM  GILBERT. 


bodies  and  reflecting  bodies,  the  forms  of  objects  are  neither 
apprehended  nor  reflected;  so,  too,  in  the  absence  of  mag- 
netic objects  neither  is  the  magnetic  force  imbibed  nor  is  it 
again  given  back  to  the  magnetic  body.  But  herein  does  the 
magnetic  energy  surpass  Hght, — that  it  is  not  hindered  by  any 
dense  or  opaque  body,  but  goes  out  freely  and  diffuses  its 
force  every  whither.  In  the  case  of  the  terrella  and  in  a 
spherical  loadstone  the  magnetic  energy  extends  outside  the 
body  in  a  circle ;  yet  in  the  case  of  an  oblong  loadstone  it 
does  not  extend  out  in  a  circle,  but  into  an  area  of  form  de- 
termined by  the  shape  of  the  stone,  as  in  the  stone  A,  in  the 
figure,  the  energy  reaches  to  the  limits  FCD,  everywhere  equi- 
distant from  the  stone  A. 


CHAPTER  VIII. 

OF  THE  GEOGRAPHY  OF  THE  EARTH  AND  THE  TERRELLA. 

We  have  next  to  speak  of  magnetic  circles  and  magnetic 
limits,  so  that  what  follows  later  may  be  better  understood. 
Astronomers,  in  order  to  account  for  and  observe  the  move- 


GEOGRAPHY  OF   THE  EARTH.  12$ 

merits  of  the  planets  and  the  revolution  of  the  heavens,  as  also 
more  accurately  to  describe  the  heavenly  order  of  the  fixed 
stars,  have  drawn  in  the  heavens  certain  circles  and  bounds, 
which  geographers  also  imitate  so  as  to  map  out  the  diversi- 
fied superficies  of  the  globe  and  to  delineate  the  fairness  of 
the  several  regions.  In  a  different  sense  we  accept  those 
bounds  and  circles,  for  we  have  discovered  many  such,  both  in 
the  terrella  and  in  the  earth;  but  these  are  determined  by 
nature  itself,  and  are  not  merely  imaginary  lines.  Geographers 
make  a  division  of  the  earth  chiefly  by  defining  the  equator 
and  the  poles  ;  and  these  bounds  are  set  and  defined  by  nature. 
Meridians,  too,  indicate  tracks  from  pole  to  pole,  passing 
through  fixed  points  in  the  equator ;  along  such  lines  the  mag- 
netic force  proceeds  and  gives  direction.  But  the  tropics  and 
the  arctic  circles,  as  also  the  parallels  of  latitude,  are  not  nat- 
ural bounds  described  on  the  earth ;  yet  all  these  parallel  cir- 
cles indicate  that  a  certain  conformity  between  themselves 
exists  among  regions  of  the  earth  situate  in  the  same  latitude 
or  diametrically  opposite  to  them.  All  these  are  of  service  to 
mathematicians  in  constructing  globes  and  maps.  Thus  such 
circles  are  of  use  in  the  terrella,  but  they  need  not  be  drawn 
as  geographers  draw  them — on  the  surface,  for  the  loadstone 
may  be  perfectly  even  and  uniform  all  over.  Nor  are  there 
any  "  upper"  or  "  lower"  parts,  in  the  terrestrial  globe,  as  there 
are  also  none  in  the  terrella,  save  perhaps  that  one  may  choose 
to  call  these  parts  "  upper"  which  are  at  the  periphery  and 
those  "  lower"  which  are  nigher  the  centre. 


126  WILLIAM  GILBERT. 

CHAPTER   IX. 

OF  THE  EQUINOCTIAL  CIRCLE  OF  EARTH  AND  TERRELLA. 

The  equinoctial  circle  imagined  by  astronomers,  which  is 
equidistant  from  both  poles  and  divides  the  earth  in  the  mid- 
dle, measures  the  movements  of  their  primum  mobile  or  tenth 
sphere,^  and  is  called  the  zone  of  th.Q  primum  mobile  ;  it  is  called 
"  equinoctial "  because  when  the  sun  is  in  this  circle — which 
must  happen  twice  a  year — the  days  are  of  equal  length  with 
the  nights.  This  circle  is  designated  also  cequidialis ;  hence 
the  Greeks  give  it  the  name  iarj^xefuvoz  (which  means  the 
same,  "  equal  day  ").  And  it  is  also  well  called  "  equator,"  for 
it  divides  the  whole  globe  of  the  earth  from  pole  to  pole  in 
two  equal  parts.  To  the  terrella  also  is  justly  assigned  an 
equator  whereby  its  power  is  distributed  between  two  parts. 
By  the  plane  of  this  equator,  as  it  passes  through  the  centre, 
the  whole  terrella  is  divided  into  two  parts  equal  in  mass  and 
in  verticity,  and  imbued  with  equal  energy,  as  though  a  wall 
stood  betwixt  the  two  verticities. 


CHAPTER   X. 

THE  earth's  magnetic  MERIDIANS. 

Geographers  have  devised  meridians  for  the  purpose  of 
distinguishing  the  longitude  and  latitude  of  regions.     But  the 

*  Y ox  primum  mobile,  see  Book  VI,  Chapter  III. 


PARALLELS.  12/ 

magnetic  meridians  are  numberless,  and,  even  as  the  earth's 
meridians,  they  pass  through  fixed  and  opposite  points  in  the 
equator  and  through  the  poles.  On  them  also  is  magnetic 
latitude  measured.  By  means  of  them  we  understand  decli- 
nations ;  and  along  them  there  is  a  fixed  direction  toward  the 
poles,  except  when  the  magnetic  body  for  any  cause  varies, 
and  is  jostled  out  of  the  right  course.  The  meridian  com- 
monly called  magnetic  is  not  properly  magnetic,  neither  is  it 
a  meridian,  but  is  supposed  to  pass  through  the  limits  of 
variation  in  the  horizon.  Variation  is  in  fact  a  faulty  devia- 
tion from  the  meridian  in  various  places  it  is  not  fixed  or  con- 
stant in  any  meridian.' 


CHAPTER   XI. 


PARALLELS. 


In  parallel  circles  the  same  energy  and  equal  potency  is 
seen  throughout,  when  different  magnetic  bodies  are  placed 
on  one  and  the  same  parallel,  either  of  the  earth  or  of  the 
terrella.  For  the  bodies  are  at  equal  distances  from  the  poles 
and  have  equal  changes  of  declination,  and  are  attracted  and 
held  and  come  together  under  the  action  of  like  forces ;  just 
as  regions  of  the  earth  on  the  same  parallel,  though  they  may 
differ  in  longitude,  are  said  to  have  still  the  same  quantity  of 
daylight  and  the  same  climate. 

'  Nicolao  Cabeo,  Philosophia  Magnetica,   1629,   Lib.  Ill,  Cap.  VI,   page 
211. 


128  WILLIAM  GILBERT. 

CHAPTER   XII. 

THE  MAGNETIC   HORIZON. 

An  horizon  is  a  great  circle  separating  the  things  seen 
from  those  that  are  out  of  sight,  as  one  half  of  the  heavens  is 
always  plainly  visible  while  another  half  is  always  hid.  So  it 
seems  to  us  by  reason  of  the  great  distance  of  the  starry 
sphere;  yet  the  difference  is  in  the  ratio  of  the  earth's  semi- 
diameter  to  the  semi-diameter  of  the  starry  heavens — a  differ- 
ence not  perceived  by  the  senses.  But  we  take  the  magnetic 
horizon  to  be  a  plane  perfectly  level  throughout,  tangent  to 
the  earth  or  to  the  terrella  at  the  place  of  the  region,  with 
which  plane  the  semi-diameter,  whether  of  the  earth  or  of  the 
terrella,  being  extended,  makes  right  angles  on  all  sides.  Such 
a  plane  is  to  be  imagined  for  the  earth,  and  for  the  terrella 
likewise,  for  the  sake  of  magnetic  proofs  and  demonstrations. 
For  we  are  considering  the  bodies  themselves,  and  not  the 
general  aspects  of  the  world.  Therefore,  not  with  reference  to 
sight — for  that  varies  according  to  the  elevation  of  regions — 
we  assume  in  magnetic  demonstrations  a  sensible  horizon,  not 
what  is  called  by  astronomers  the  rational  horizon. 


CHAPTER  XIII. 

OF  THE  MAGNETIC  AXIS  AND  POLES.. 

A  LINE  drawn  through  the  centre  of  the  earth  (or  of  the 
terrella)  to  the  poles  is  called  the  axis.     The  poles  are  so 


COITION  STRONGER  AT   THE  POLE.  1 29 

called  by  the  Greeks  (ttoAoz,  and  rov  TtoXeiv — poloiirorapolein, 
to  revolve),  and  by  the  Latins  cardines  (hinges,  pivots)  and 
vertices  (centres  of  a  whirling  motion)  ;  and  these  names  were 
given  to  signify  that  the  world  rotates  and  is  ever  whirling. 
We  propose  to  show  that  the  earth  and  the  terrella  are  by 
the  magnetic  force  made  to  revolve  round  these  poles,  whereof 
that  one  in  the  earth  which  points  to  Cynosura^  is  called  the 
North,  the  Boreal,  or  the  Arctic  pole ;  the  opposite  one  is 
called  the  South,  Austral,  or  Antarctic  pole.  And  neither  in 
earth  nor  in  terrella  do  the  poles  exist  merely  for  the  sake  of 
rotation ;  they  are  furthermore  reference  points  of  direction 
and  of  position  {consist endi), — on  the  one  hand  towards  one's 
destination  on  the  earth,  and  on  the  other  hand  as  regards 
their  angular  distance  {turn  versus  destinatas  mundi  regiones). 


CHAPTER   XIV. 

WHY  THE  COITION  IS  STRONGER  AT  THE  POLE  THAN  IN 
THE  PARTS  BETWEEN  EQUATOR  AND  POLE;  AND  THE 
RELATIVE  POWER  OF  COITION  IN  DIFFERENT  PARTS  OF 
THE  EARTH  AND  THE  TERRELLA. 

We  have  already  shown  that  the  supreme  attractional 
power  is  at  the  pole,  while  the  weaker  and  more  sluggish 
power  is  in  the  parts  nigh  the  equator.  And  as  in  the  decli- 
nation it  is  seen  that  this  ordering  and  rotating  force  increases 
as  we  advance  from  the  equator  to  the  poles,  so  too  does  the 
coition  of  magnetic  bodies  grow  stronger  by  the  same  degrees 

»  Cynosura— Cynosure— the  constellation  of  the  Lesser  Bear  ( £/rja  J/wK^r) 
containing  the  polar  star. 


130  WILLIAM  GILBERT, 

and  in  the  same  proportion.  For  at  points  remote  from  the 
pole  the  loadstone  does  not  pull  magnetic  bodies  in  a  right 
line  toward  its  centre,  but  they  tend  to  it  obliquely,  and 
obliquely  are  attracted.  For  as  a  very  small  chord  of  a  circle 
differs  from  the  diameter,  by  so  much  do  differ  the  attractional 
powers  of  different  parts  of  the  terrella.  For  inasmuch  as  the 
attraction  is  a  coition  to  a  body,  and  magnetic  bodies  come 
together  owing  to  their  natural  tendency  to  turn  to  each  other, 
in  the  diameter  drawn  from  pole  to  pole  a  body  impinges  on  the 
loadstone  in  a  right  line  ;  but  not  so  in  other  parts.  Therefore 
the  less  it  turns  toward  the  body,  the  less  and  the  more  weak 
is  the  coition  and  the  cohesion.     Let  ab  be  the  poles.     An 


iron  bar  or  the  other  magnetic  body  c  is  attracted  at  e ;  yet 
the  end  that  is  pulled  does  not  tend  toward  the  centre  of  the 
loadstone,  but  obliquely  toward  the  pole,  and  a  chord  drawn 
from  that  end  obliquely  in  the  direction  in  which  the  body  is 
attracted  is  a  short  one ;  the  strength  of  the  coition  therefore 
is  less,  and  so  too  the  attracted  object  turns  at  a  less  angle  to 
the  terrella.  But  as  from  a  body  at  /  a  longer  chord  pro- 
ceeds, so  the  action  there  is  stronger.     At  g  the  chord  is  still 


MAGNETIC  FORCE  IMPARTED    TO  IRON.  I3I 

longer.  At  a  (the  pole)  it  is  longest  of  all  (for  the  diameter  is 
the  longest  line),  and  thither  do  all  the  parts  send  their  forces : 
there  stands,  as  it  were,  the  citadel,  the  judgment-seat,  of  the 
whole  region, — not  that  the  pole  holds  this  eminence  in  its  own 
right,  but  because  it  is  the  depository  of  forces  contributed  to 
it  by  all  the  other  parts ;  it  is  like  soldiers  bringing  reinforcement 
to  their  commander.  Hence  a  rather  oblong  loadstone  attracts 
better  than  a  spherical  one,  if  its  length  stretch  from  pole 
to  pole,  and  yet  the  two  may  be  from  the  same  mine,  and  be 
of  equal  size  and  volume.  The  way  is  longer  from  one  pole  to 
the  other  in  the  oblong  stone,  and  the  force  supplied  by  the 
other  parts  are  not  so  scattered  as  in  a  spherical  loadstone 
and  the  terrella ;  they  are  better  massed  and  united,  and  thus 
united  they  are  stronger  and  greater.  But  a  flat  or  oblong 
loadstone  is  much  less  effective  when  the  length  is  in  the  direc- 
tion of  the  parallels,  and  the  pole  ends  neither  in  a  point  nor 
in  a  circle  or  sphere,  but  lies  flat  on  a  plane  surface  so  as  to 
be  held  for  something  abject  and  of  no  account,  for  its  unfit 
and  unadaptable  form. 


CHAPTER    XV. 

THE  MAGNETIC  FORCE  IMPARTED  TO  IRON  IS  MORE  APPAR- 
ENT IN  AN  IRON  ROD  THAN  IN  AN  IRON  SPHERE  OR 
CUBE,  OR  IRON  OF  ANY  OTHER  SHAPE. 

It  has  been  already  said  that  an  oblong  loadstone  lifts  a 
greater  weight  of  iron :  so  in  a  long  piece  of  iron  rubbed  with 
a  loadstone  the  magnetic  force  is  stronger  if  the  poles  are  at 
the  ends ;   for  the  magnetic  forces,  which  are  sent  to  both 


132  WILLIAM  GILBERT. 

ends  from  the  poles,  are  concentrated  at  the  narrow  terminals, 
and  not  diffused.  In  square  and  other  angular  figures  the 
force  is  scattered,  nor  does  it  proceed  in  right  lines  or  along 
suitable  arcs.  The  iron  sphere,  too,  though  it  hath  the  figure 
of  the  earth,  still  has  less  attraction  for  magnetic  bodies  for 
the  same  reason ;  hence  an  excited  iron  spherule  acts  with 
less  force  on  iron  than  does  a  magnetized  bar  of  the  same 
weight. 


CHAPTER  XVI. 

THAT  MOTION  IS  PRODUCED  BY  THE  MAGNETIC  FORCE 
THROUGH  SOLID  BODIES  INTERPOSED  :  OF  THE  INTER- 
POSITION  OF  A   PLATE   OF    IRON. 

An  iron  wire  passed  through  a  suitable  piece  of  cork,  or  a 
needle  poised  on  a  point  or  in  a  mariner's  compass,  is  set  in 
motion  when  a  loadstone  is  brought  near  it  or  is  passed 
beneath  it,  though  the  water,  the  vessel,  or  compass-box  stand 
between.  No  hindrance  is  offered  by  thick  boards,  or  by  walls 
of  pottery  or  marble,  or  even  of  metals  :  there  is  naught  so 
solid  as  to  do  away  with  this  force  or  to  check  it,  save  a  plate 
of  iron.  Whatever  substances  are  interposed,  however  dense 
they  be,  as  they  do  not  annul  the  force  nor  obstruct  its  path, 
so  do  they  in  no  wise  hinder  or  lessen  or  retard.  Nor  is  the 
whole  of  the  force  suppressed  by  a  plate  of  iron,  but  in  part 
diverted.  For  when  the  force  enters  the  middle  of  an  iron 
plate  placed  within  the  sphere  of  magnetic  influence  or  directl)^ 
*  over  the  pole  of  the  loadstone,  that  force  is  distributed  chiefly 
to  the  extremities,  so  that  the  rim  of  a  circular  plate  of  suit- 


MOTION  PRODUCED  BY  MAGNETIC  FORCE.  1 33 

able  size  attracts  pieces  of  iron  wire  at  all  points.     The  same 
is  seen  in  a  long  iron  rod  rubbed  with  a  loadstone  in  the  mid-* 


die  ;  it  has  the  same  verticity  at  both  ends.  In  the  figure, 
CD  is  a  long  rod  magnetized  in  the  middle  by  the  north  pole 
E  \  C  is  a  south  end  or  south  pole,  and  D  is  another  south  end. 
But  here  note  the  singular  fact,  that  a  needle  magnetized  by 
that  pole  turns  to  that  pole,  though  the  round  plate  stands 
between,  the  plate  not  hindering,  but  the  attraction  being  only* 
weaker ;  for  the  force  is  scattered  to  the  extremities  of  the 
plate,  and  departs  from  the  straight  track,  but  yet  the  plate  in 
its  middle  retains  the  same  verticity  with  the  pole  when  it  is 
nigh  it  and  alongside  it :  hence  does  the  needle  magnetized  by 
the  same  pole  tend  to  the  centre  of  the  plate.  If  the  loadstone 
is  a  weak  one,  the  needle  hardly  turns  if  an  iron  plate  be  inter- 
posed ;  for,  being  diffused  out  to  the  extremities  of  the  plate, 
the  loadstone's  energy  is  less  able  to  pass  through  the  centre. 
But  let  the  plate  be  magnetized  in  the  middle  by  the  pole,  and  * 
then  let  it  be  removed  beyond  the  loadstone's  sphere  of  in- 
fluence, and  you  shall  see  the  point  of  the  same  needle  go  in 
the  contrary  direction  and  quit  the  centre  of  the  plate,  which 
before  it  sought :  for  outside  of  the  sphere  of  influence  the  plate 
has  the  contrary  verticity,  but  near  the  loadstone  it  has  the 
same  ;  for  near  the  loadstone  the  plate  is  as  it  were  part  of  the 
loadstone  and  has  the  same  pole.     Let   A  be  an  iron   plate 


134  WILLIAM  GILBERT. 

near  a  pole  ;  B  a  needle  with  point  tending  toward  the  centre 
of  the  plate,  which  plate  has  been  magnetized  by  the  pole  C 
of  a  loadstone.  Now  if  the  same  plate  be  placed  outside  the 
sphere  of  magnetic  influence,  the  point  of  the  needle  will  noL 
turn  to  its  centre,  but  only  the  crotch  (the  other  end)  of  the 


same  needle.     But  an  iron  sphere  interposed  (if  it  be  not  too 

*  large)  attracts  the  point  of  the  needle  at  the  other  side  of  the 
stone,  for  the  verticity  of  that  side  is  the  same  as  that  of  the 
adjoining  pole  of  the  loadstone.  And  this  turning  of  the 
needle's  point  (i.e.,  the  end  of  it  magnetized  by  contact  with 
that  pole)  and  of  its  cross  (other  end)  at  a  considerable  distance 

♦  takes  place  with  an  iron  sphere  interposed,  whereas  it  would 
not  take  place  at  all  were  the  space  between  vacant ;  for  the 
magnetic  force  travels  through  bodies  and  is  continued  on  by 
them.  Let  A  he  a.  terrella,  B  an  iron  sphere,  F  a  needle 
between  the  two  bodies,  with  its  point  magnetized  by  the  pole 
C.  In  the  second  figure  A  is  the  terrella,  C  a  pole,  B  an  iron 
sphere :  the  needle  tends  toward  C,  the  terrella's  pole,  through 
the  iron  sphere.  The  needle  thus  placed  between  terrella  and 
sphere  vibrates  more  forcibly  toward  the  pole  of  the  terrella, 
because  the  loadstone  imparts  instantaneous  verticity  to  the 
opposite  sphere.  The  earth's  efficiency  is  the  same,  produced 
by  the  same  cause.  For  if  in  a  thick  box  made  of  gold  (the 
densest  of  metals)  or  glass,  or  marble,  you  put  a  needle  free  to 


MOTION  PRODUCED  BY  MAGNETIC  FORCE.  1 35 

revolve,  that  needle,  in  spite  of  the  box,  will  show  that  its 
forces  are  most  closely  allied  to  and  unified  with  those  of  the 
earth ;  of  its  own  accord  and  instantly,  regardless  of  the  box 


that  prisons  it,  it  turns  to  its  desiderated  points  of  north  and 
south.  And  it  does  the  same  though  it  be  shut  up  in  iron* 
vaults  sufficiently  roomy.  Whatever  bodies  are  produced  here 
on  the  earth  or  are  manufactured  from  nature's  products  by 
art,  all  consist  of  the  matter  of  the  globe  :  such  bodies  do  not 
interfere  with  the  prime  potencies  of  nature  derived  from  the 
primary  form  ;  nor  can  they  withstand  them,  save  by  contrary 
forms.  But  no  forms  of  mixed  bodies  are  inimical  to  the  innate 
primary  form,  though  some  of  them  oft  do  not  accord  among 
themselves.  On  the  other  hand,  in  all  the  bodies  that  have  a 
material  cause  of  attraction  (e.g.,  amber,  jet,  sulphur)  action  is 
hindered  by  interposition  of  a  body  (as  paper,  leaves,  glass,  etc.), 
and  the  way  is  obstructed  and  blocked  so  that  that  which  is 
exhaled  cannot  reach  the  light  body  that  Is  to  be  attracted. 
But  coition  and  movement  of  the  earth  and  the  loadstone, 
though  corporeal  hindrances  be  interposed,  are  shown  also  in 
the  efficiencies  of  other  chief  bodies  that  possess  the  primary 


I30  WILLIAM  GILBERT. 

form.  The  moon,  more  than  the  rest  of  the  heavenly  bodies, 
is  in  accord  with  the  inner  parts  of  the  earth  because  of  her 
nearness  and  her  likeness  of  form.  The  moon  causes  the  move- 
ment of  the  waters  and  the  tides  of  ocean  ;  makes  the  seashore 
to  be  covered  and  again  exposed  twice  between  the  time  she 
passes  a  given  point  of  the  heavens  and  reaches  it  again  in  the 
earth's  daily  rotation  :  this  movement  of  the  waters  is  produced 
and  the  seas  rise  and  fall  no  less  when  the  moon  is  below  the 
horizon  and  in  the  nethermost  heavens,  than  when  she  is  high 
above  the  horizon.  Thus  the  whole  mass  of  the  earth,  when 
the  moon  is  beneath  the  earth,  does  not  prevent  the  action  of 
the  moon  ;  and  thus  in  certain  positions  of  the  heavens,  when 
the  moon  is  beneath  the  horizon,  the  seas  nearest  to  our  coun- 
tries are  moved,  and,  being  stirred  by  the  lunar  power  (though 
not  struck  by  rays  nor  illumined  by  light),  they  rise,  approach 
with  great  impetus,  and  recede.  Of  the  reason  of  this  we  will 
treat  elsewhere  :  sufiEice  it  here  just  to  have  touched  the  thresh- 
old of  the  question.  Hence,  here  on  earth,  naught  can  be 
held  aloof  from  the  magnetic  control  of  the  earth  and  the  load- 
stone, and  all  magnetic  bodies  are  brought  into  orderly  array 
by  the  supreme  terrene  form,  and  loadstone  and  iron  sympa- 
thize with  loadstone  though  solid  bodies  stand  between.' 


^  In  connection  with  the  increased  energy  which  magnets  acquire  by  being 
armed,  that  is,  fitted  with  a  cap  of  polished  iron  at  each  pole,  Dr.  Whewell 
remarks,  that  it  is  only  at  a  later  period  any  notice  was  taken  "  of  the  distinc- 
tion which  exists  between  the  magnetical  properties  of  soft  iron  and  of  hard 
steel; — the  latter  being  susceptible  of  being  formed  into  artificial  magnets ,  with 
permanent  poles  ;  while  soft  iron  is  only  passively  magnetic,  receiving  a  tempo- 
rary polarity  from  the  action  of  a  magnet  near  it,  but  losing  this  property  when 
the  magnet  is  removed.  About  the  middle  of  the  last  century  various  methods 
were  devised  of  making  artificial  magnets,  which  exceeded  in  power  all  mag- 
netic bodies  previously  known."  ("Hist,  of  Ind.  Sciences,"  1859,  Vol.  II,  page 
220.) 


IRON  HELMET  OF   THE  LOADSTONE.  1 37 


CHAPTER  XVII. 

OF  THE  IRON  HELMET  (CAP)  OF  THE  LOADSTONE,  WHERE- 
WITH IT  IS  ARMED  AT  THE  POLE  TO  INCREASE  ITS 
ENERGY  ;   EFFICIENCY   OF  THE   SAME.' 

A  CONCAVE  hemisphere  of  thin  iron,  a  finger's  width  in 
diameter,  is  applied  to  the  convex  polar  superficies  of  a  load- 
stone and  properly  fastened  ;  or  an  iron  acorn-shaped  ball  ris- 
ing from  the  base  into  an  obtuse  cone,  hollowed  out  a  little  and 
fitted  to  the  surface  of  the  stone,  is  made  fast  to  the  pole. 
The  iron  must  be  the  best  (steel),  smooth,  polished,  and  even. 
Fitted  with  this  contrivance,  a  loadstone  that  before  lifted 
only  4  ounces  of  iron  will  now  lift  12  ounces.  But  the  greatest 
force  of  the  co-operating  or  rather  unified  matter  is  seen 
when  two  loadstones  fitted  with  these  projections  are  so  joined" 
as  mutually  to  attract  and  lift  each  other :  thus  may  a  weight 
of  20  ounces  be  lifted,  though  either  stone  unarmed  would  Hft 
only  4  ounces.  Iron  is  held  faster  by  an  armed  loadstone  than 
by  one  not  armed,  and  hence  it  lifts  greater  weights,  because 
iron  clings  more  strongly  to  the  armed  stone  :  for,  by  the  con- 
tiguous presence  of  the  loadstone,  the  iron  of  the  armature 
and  the  iron  attracted  are  bound  fast  together  ;  and  when  the 
armature  has  imbibed  the  magnetic  energy  by  reason  of  the 
presence  of  the  loadstone,  and  another  piece  of  iron  adjoining 
at  the  same  time  derives  force  from  the  presence  of  a  loadstone, 
the  two  unite  energetically.     Hence  when  two  powerful  arma- 


'  Dr.    J.    Lament's    "  Handbuch    des    Magnetismus,"   Leipzig   1867,  page 
53. 


138  WILLIAM  GILBERT. 

tures  are  in  contact  they  cohere  strongly.  This  is  proved  in  Book 
III,  Chap.  IV,  by  iron  rods  cohering,  as  also  where  we  men- 
tion the  transformation  of  steel-filings  into  a  concreted  mass» 
For  this  reason  iron  situate  near  a  loadstone  takes  away  from 
it  pieces  of  iron  of  suitable  weight,  provided  only  it  be  in  con- 
tact with  them  ;  else,  however  near  they  may  be,  it  does  not 
match  them.  For  masses  of  magnetic  iron  do  not,  within  the 
field  of  a  loadstone  or  near  a  loadstone,  attract  more  strongly 
than  the  loadstone  attracts  any  iron ;  but  once  they  are  in  con- 
tact with  each  other  they  unite  more  strongly,  and  become  as 
it  were  clamped  together,  though  with  the  same  forces  at  work 
the  substance  remains  the  same/ 


CHAPTER   XVIII. 

AN   ARMED   LOADSTONE    DOES     NOT     ENDOW   WITH    GREATER 
FORCE   MAGNETIZED   IRON   THAN   DOES   AN   UNARMED   ONE. 

Take  two  pieces  of  iron,  one  magnetized  with  an  armed 
and  the  other  with  an  unarmed  loadstone,  and  apply  to  one 
of  them  a  weight  of  iron  proportioned  to  its  powers :  the  other 
loadstone  will  lift  the  same  weight,  and  no  more.  Two  needles 
also  turn  with  the  same  velocity  and  constancy  toward  the 
poles  of  the  earth,  though  one  needle  may  have  been  touched 
by  an  armed  magnet  and  the  other  by  one  unarmed. 

*  Sir  Kenelm  Digby,  "The  Nature  of  Bodies,"  1645,  Chap.  XXII,  page 
243;  Jacobi  Rohaulti,  Physica,  Londini  1718,  Par.  Ill,  Cap.  VIII,  p.  403,  or 
the  English  translation  by  Dr.  Clarke,  London,  1728,  Vol.  II,  page  181;  Ath. 
Kircheri,  Magnes ;  sive  de  arte  Magnetica,  1643,  Lib.  I,  Pars  II,  page  63; 
Nicolao  Cabeo,  Philosophia  Magnetica,  1629,  Lib.  IV,  Cap.  XLII,  page  407. 


AN  ARMED  MAGNET  LIFTS  ANOTHER. 


139 


CHAPTER  XIX. 


THAT  UNITION  IS  STRONGER  WITH  AN  ARMED  LOADSTONE  ; 
HEAVIER  WEIGHTS  ARE  THUS  LIFTED  ;  THE  COITION  IS 
NOT   STRONGER,   BUT   COMMONLY   WEAKER. 

That  an  armed  loadstone  lifts  a  greater  weight  is  evident 
to  all ;  but  iron  is  drawn  from  the  same  dis- 
tance, or  rather  from  a  greater  distance,  to 
the  loadstone  when  the  stone  is  without  the 
iron  helmet.  This  is  to  be  tried  with  two 
pieces  of  iron  of  the  same  weight  and  form  at  * 
equal  distance,  or  with  one  and  the  same 
needle,  tested  first  with  the  armed  then  with 
the  unarmed  stone,  at  equal  distances. 


CHAPTER  XX. 

THAT  AN  ARMED  MAGNET  LIFTS  ANOTHER, 
AND  THAT  ONE  A  THIRD:  THIS  HOLDS 
GOOD  THOUGH  THERE  BE  LESS  ENERGY 
IN  THE   FIRST. 

Armed  loadstones  duly  joined  together 
cohere  firmly  and  form  one  ;  and  though  the 
first  be  weak,  the  second  nevertheless  clings  to 
it,  not  alone  with  the  force  of  the  first,  but  of 
the  second,  the  stones  thus  helping  each  other : 
to  the  second  a  third  will  often  cling,  and  with  strong  load- 
stones a  fourth  to  the  third. 


I40  WILLIAM  GILBERT. 


CHAPTER   XXI. 

THAT  WHEN  PAPER  OR  OTHER  MEDIUM  IS  INTERPOSED,  AN 
ARMED  LOADSTONE  DOES  NOT  LIFT  MORE  THAN  ONE 
UNARMED. 

It  has  been  shown  above  that  an  armed  loadstone  does  not 
attract  at  a  greater  distance  than  an  unarmed  one,  but  that  it 
lifts  a  greater  quantity  of  iron,  if  it  be  in  contact  with  the  iron 
and  continuous  therewith.  But  put  a  leaf  of  paper  between, 
and  this  intimate  coherence  is  hindered,  nor  are  objects  of 
iron  held  together  by  the  action  of  the  loadstone. 


CHAPTER   XXII. 

THAT  AN  ARMED  LOADSTONE  DOES  NOT  ATTRACT  IRON  MORE 
THAN  AN  UNARMED  ONE  ;  AND  THAT  THE  ARMED  STONE 
IS  MORE  STRONGLY  UNITED  TO  THE  IRON,  IS  SHOWN  BY 
MEANS  OF  AN  ARMED  LOADSTONE  AND  A  CYLINDER  OF 
POLISHED   IRON. 

On  a  plane  surface  lay  a  cylinder  too  heavy  for  the  un- 
armed loadstone  to  lift ;  then,  with  paper  between,  apply  at 
the  middle  of  the  cylinder  the  pole  of  an  armed  loadstone :  if 
the  cylinder  is  pulled  by  the  loadstone,  it  follows  after  it  with 
rolling  motion ;  but  when  there  is  no  paper  between,  the  cylin- 
der, joined  to  the  loadstone,  is  pulled  by  it,  and  does  not  roll 


ARMED  AND    UNARMED  LOADSTONES. 


141 


% 


at  all.  But  if  the  same  loadstone  be  unarmed,  it  pulls  the  roll- 
ing cylinder  with  the  same  velocity  as  does  an  armed  loadstone 
with  paper  between,  or  wrapped  in  paper. 

Armed  loadstones  of  different  weights,  force,  and  shape,  but  * 
out  of  the  same  mine,  show  an    equal   degree    of 
strength   in    adhering   to    or  hanging  from  iron 
objects  of  suitable  size  and  shape.       The    same 
is  true  of    unarmed  ones.      A   suitable  piece  of* 
iron  applied  to    the  under  side    of  a  loadstone 
that  hangs  from  a  magnetic  body  heightens  the* 
energy  of   the  loadstone,  so  that   it  clings  with 
greater  force.     For  a  pendent   loadstone   clings 
faster   to    the    body   above,    to   which   it   is   at- 
tached, when  a  piece  of  iron  is  applied  and  hangs 
from  it,  than  when  a  piece  of  lead  or  other  non- 
magnetic material  is  fastened  to  it. 

A  loadstone,  whether  armed  or  not,  attached 
by  its  proper  pole  to  the  pole  of  another  load-* 
stone,  armed  or  not,  makes  that  other  lift  a 
greater  weight  at  its  opposite  end.  The  same 
thing  is  seen  when  iron  is  applied  to  the  pole  of 
a  loadstone,  viz.,  the  opposite  pole  carries  a  greater 
weight  of  iron  :  thus,  as  in  the  figure,  the  load- 
stone with  a  bar  of  iron  superposed  carries  the 
bar  below,  but  cannot  carry  it  if  the  upper  piece 
be  removed.  Magnetic  bodies  in  conjunction  * 
form  one  magnetic  body ;  hence,  the  mass  increasing,  the  mag- 
netic energy  increases  also. 

An  armed  loadstone,  as  also  an  unarmed  one,  leaps  more* 
quickly  to  a  large  mass  of  iron  and  combines  with  it  more 
strongly  than  with  a  small  mass. 


142  WILLIAM  GILBERT. 


CHAPTER   XXIII. 

THE  MAGNETIC  FORCE  MAKES  MOTION  TOWARD    UNION,   AND 
WHEN   UNITED   CONNECTS   FIRMLY. 

Magnetized  objects  cohere  well  and  duly  to  one  another 

*  according  to  their  forces.  Pieces  of  iron  in  the  presence  of  a 
loadstone,  though  not  in  contact  with  it,  come  together, 
eagerly  seek  and  seize  one  another,  and  when  in  conjunction 

♦are,  as  it  were,  glued  together.  Iron  dust  or  iron  reduced  to  a 
powder,  packed  in  paper  tubes,  and  placed  on  the  meridian  of 
a  loadstone  or  merely  brought  near  it,  coalesces  into  one  mass, 

*  and  in  an  instant  the  many  particles  come  together  and  com- 
bine ;  and  the  multitude  of  united  grains  acts  on  a  piece  of  iron 

*  and  attracts  it,  as  though  they  formed  but  one  continuous  rod 
of  iron,  and  take  the  north  and  south  direction  when  laid  on 
the  loadstone.  But  if  they  be  taken  away  from  the  stone  to 
any  distance,  the  particles,  resolved  again  to  their  original  con- 
dition, separate,  and  each  stands  alone:  thus  it  is  that  the  foun- 
dations of  the  earth  are  conjoined,  connected,  held  together, 
magnetically.  So  let  not  Ptolemy  of  Alexandria,  and  his  fol- 
lowers and  our  philosophers,  maintain  that  the  earth  will  go  to 
pieces,  neither  let  them  be  alarmed  if  the  earth  spins  round  in 
a  circle. 

Iron-filings  when  made  hot  are  attracted  by  the  loadstone 

not  so  strongly  nor  from  as  great  a  distance  as  if  they  were 

*not  heated.     A  loadstone  subjected  to  any  great  heat  loses 

some  of  its  energy ;  for  its  humor  is  dissipated,  and  so  its  pecul- 

*  iar  nature  is  marred.  So,  too,  a  mass  of  iron-filings,  if  roasted 
in  a  reverberatory  furnace  and  changed  to  Crocus  Martis,  is  not 


IRON  HANGS  SUSPENDED  IN  AIR.  I43 

attracted  by  a  loadstone  ; '  but  if  it  has  not  been  very  highly 
heated,  not  quite  wasted,  it  clings  to  loadstone,  though  more* 
feebly  than  iron  that  has  not  been  put  in  jfire.  For  Crocus 
Martis  has  nothing  of  the  form  of  iron  left ;  but  metal  that  has 
been  made  hot  takes  heat  from  the  fire,  and  in  its  vitiated  sub- 
stance the  magnetic  powers  are  less  powerfully  awakened  by  the 
loadstone,  and  iron  that  has  quite  lost  its  nature  is  not  attracted 
by  the  loadstone. 


CHAPTER   XXIV. 

THAT  IRON  WITHIN  THE  FIELD  OF  A  LOADSTONE  HANGS 
SUSPENDED  IN  AIR,  IF  ON  ACCOUNT  OF  AN  OBSTACLE  IT 
CANNOT   COME   NEAR. 

Iron  within  the  magnetic  field  tends  toward  the  points  of  = 
the  stone  that  have  the  most  energy,  if  it  be  not  hindered  by 

'  Crocus  Martis,  or  "Saffron  of  Mars,"  already  mentioned,  Book  I,  Chap. 
XV,  was  formed  in  ancient  pharmacy  by  deflagrating  iron  filings  with  nitre 
and  washing  the  residue.  (Brande's  "Manual  of  Chemistry,"  Vol.  I,  page 
715.)  Geber  mentions  oxide  of  copper  under  the  name  of  ces  ustum,  the  red 
oxide  of  iron  under  the  name  of  crocus  of  iron.  (Dr.  Thomson,  "Hist,  of 
Chem.,"  Vol.  I,  page  130.)  We  read  in  Sir  Thomas  Brown's  Pseudoloxia 
Epidemica,  1658,  page  71  :  "  It  is  likewise  true  what  some  have  delivered  of 
Crocus  Martis,  that  is,  steel  corroded  with  vineger,  sulphur,  or  otherwise,  and 
after  reverberated  by  fire.  For  the  loadstone  will  not  at  all  attract  it,  nor  will 
it  adhere,  but  lie  therein  like  sand.  This  to  be  understood  of  Crocus  Martis  well 
reverberated,  and  into  a  violet  colour;  for  common  chalyhs  prcsparatus,  or  cor- 
roded and  powdered  steel,  the  loadstone  attracts  like  ordinary  filings  of  iron  ; 
and  many  times  most  of  that  which  passeth  for  Crocus  Martis.  So  that  this 
way  may  serve  as  a  test  of  its  preparation  ;  after  which  it  becometh  a  very 
good  medicine  in  fluxes.  The  like  may  be  afiirmed  of  flakes  of  iron  that  are 
rusty  and  begin  to  tend  unto  earth.  For  their  cognation  then  expireth,  and  the 
loadstone  will  not  regard  them."  Consult  Lazarus  Erckern's  Aula  Subterranea, 
Franckfurt  1672,  page  294,  or  Sir  J.  Pettus'  "  Heta  Minor,"  London  1683, 
although,  according  to  Dr.  Thomson,  the  translation  is  a  very  bad  one. 


144  WILLIAM  GILBERT. 

force  or  by  the  matter  of  an  intervening  body ;  and  this  is  so 
whether  the  iron  tends  downward  to  the  loadstone,  or  seeks  it 
from  one  side  and  obliquely,  or  whether  it  leaps  up  to  it.  But 
if  on  account  of  an  obstacle  it  cannot  reach  the  stone,  it  sticks 
to  the  obstacle  and  there  remains,  yet  is  held  by  a  less  constant 
bond,  for,  owing  to  the  greater  intervals  and  distances,  the  asso- 
ciation (with  the  loadstone)  is  less  amicable.  Fracastorio,  in 
his  Chapter  VIII,  De  Sympathia,  says  that  a  piece  of  iron  will 
be  suspended  in  air  so  that  it  cannot  move  either  up  or  down 
if  a  loadstone  be  placed  above  it  that  has  an  attractive  force  on 
the  iron  equal  to  the  force  by  which  the  iron  tends  downward : 
thus  the  iron  will  stand  fixed  in  mid-air.  That  is  ridiculous : 
for  the  nearer  the  loadstone  the  greater  always  is  its  force ;  and 
hence  the  iron  that  is  lifted  ever  so  little  above  the  earth  by 
the  loadstone's  force  must  needs  be  steadily  drawn  to  it,  and 
must  cling  to  it.  Baptista  Porta  suspends  in  air  a  piece  of  iron 
(with  a  loadstone  fixed  above),  and  holds  back  the  iron  by 
means  of  a  thin  thread  fastened  to  it  beneath,  so  that  it  shall 
not  rise  to  the  stone  ; — hardly  a  very  brilliant  idea.  The  piece 
*  of  iron  is  pulled  in  a  perpendicular  line  by  the  loadstone,  though 
the  two  are  not  in  contact,  but  only  near  each  other ;  but,  as  on 
account  of  the  greater  nearness,  the  iron  mass  is  stirred  by  the 
force  that  was  lifting  it,  straightway  it  speeds  to  the  loadstone 
and  clings  to  it.  For  the  iron,  the  nearer  it  comes  to  the  load- 
stone, the  more  is  excited,  and  the  stronger  is  the  attraction. 


INTENSIFYING    THE  LOADSTONES  FORCES.  145 


CHAPTER   XXV. 

INTENSIFYING   THE   LOADSTONE'S   FORCES. 

One  loadstone  far  surpasses  another  in  energy,  for  one  will 
snatch  up  almost  its  own  weight  of  iron,  while  another  is  hardly 
able  to  move  the  smallest  particle.  All  animals  and  plants 
that  possess  life  have  need  of  victual  of  some  sort,  to  the  end 
their  powers  may  last  and  become  firmer  and  stronger.  But 
iron  is  not  attracted  by  the  loadstone,  as  Cardan  and  Alexander 
Aphrodiseus  supposed,  so  that  it  may  be  nourished  with  mor- 
sels of  it ;  neither  does  the  loadstone  gain  strength  from  iron- 
filings  as  from  a  nutritious  food.  Baptista  Porta,  having  his 
doubts  about  this  view,  and  wishing  to  make  an  experiment, 
took  a  loadstone  of  determinate  weight  and  buried  it  in  iron- 
filings  of  a  weight  not  unknown  ;  and,  after  he  had  left  it  there 
many  months,  he  found  the  stone  heavier,  the  filings  lighter. 
But  the  difference  was  so  minute  that  Porta  was  uncertain  as 
to  the  truth.  This  experiment  of  Porta's  does  not  prove  that 
the  stone  devours  anything,  nor  does  it  show  any  process  of 
nutrition,  for  minute  quantities  of  fihngs  are  easily  lost  by 
handling.  So,  too,  a  very  small  quantity  of  the  iron  dust  may 
adhere  to  some  small  part  of  the  loadstone  and  not  be  noticed, 
thus  adding  somewhat  to  the  weight  of  the  stone  ;  but  that  is 
a  superficial  accretion,  and  can  be  brushed  off  without  much 
difficulty.  Many  think  that  when  weak  and  sluggish  the  stone 
can  bring  itself  back  to  a  better  condition,  and  that  a  very 
strong  stone  can  endow  a  weaker  one  with  the  highest  degree 
of  force.     Is  it  as  when  animals  gain  strength  when  they  feed 


146  WILLIAM  GILBERT. 

and  are  filled  ?  Is  a  remedy  found  for  the  loadstone  in  addi- 
tion or  subtraction  of  something  ?  Is  there  aught  that  can 
restore  this  primary  form  or  give  it  anew?  Surely  nothing  can 
do  such  a  thing  save  what  possesses  magnetic  properties. 
Magnetic  bodies  can  restore  soundness  (when  not  totally  lost) 
to  magnetic  bodies,  and  can  give  to  some  of  them  powers 
greater  than  they  had  originally  ;  but  to  those  that  are  by  their 
nature  in  the  highest  degree  perfect,  it  is  not  possible  to  give 
further  strength.  Hence  the  more  infamous  becomes  all  the 
charlatanry  of  Paracelsus,  who  declares  that  the  loadstone's 
force  and  energy  may  be  increased  and  transformed  to  tenfold 
what  it  is  naturally.  And  the  way  of  doing  this  is,  so  to  speak, 
to  half-candescify  the  loadstone,  i.e.,  to  make  it  very  hot, 
yet  so  that  it  does  not  reach  white  heat,  and  then  immediately 
to  dip  it  in  oil  of  vitriol  made  from  the  best  Corynthian  steel, 
letting  it  become  saturated.  "  In  this  way,"  says  Paracelsus, 
"  you  can  give  to  a  loadstone  such  strength  that  it  will  pull  a 
nail  out  of  a  wall,  and  perform  many  other  the  like  marvels  im- 
possible for  a  common  loadstone."  But  a  loadstone  so  dipped 
not  only  acquires  no  force,  but  suffers  some  loss  it  already  hath. 
A  loadstone  rubbed  and  smoothed  with  steel  is  made  better. 
When  covered  with  filings  of  the  best  iron  or  pure  steel,  not 
rusty,  it  retains  its  properties.  Sometimes,  too,  a  good  strong 
loadstone  gains  some  strength  when  rubbed  on  its  opposite 
pole  with  the  pole  of  another  loadstone  :  it  takes  in  force.  In 
such  experiments  it  is  well  to  observe  the  earth's  pole,  and  to 
lay  down  in  the  direction  required  by  the  magnetic  laws  the 
stone  that  one  wishes  to  make  stronger:  this  point  we  will 
establish  hereafter.  A  strong,  large  loadstone  increases  the 
power  of  another  loadstone,  as  also  the  power  of  iron.  If,  on 
*the  north  pole  of  a  loadstone,  you  place  another  loadstone, 
the  north  pole  of  the  second  becomes  stronger,  and  a  piece  of 


INTENSIFYING    THE   LOADSTONE'S  FORCES. 


H7 


iVon  clings  like  an  arrow  to  the  north  pole  a,  and  not  at  all  to 
the  south  pole  I?.  And  the  pole  a,  when  it  is  in  a  right  line 
above  with  the  axis  of  both  loadstones,  they  being  joined  ac- 
cording to  the  magnetic  laws,  raises  the  piece  of  iron  to  the 
perpendicular :  this  it  cannot  do  if  the  larger  loadstone  be 
moved  away,  for  its  strength  is  insuflticient.     But  as  a  ball  of 


iron  on  the  pole  of  the  terrella  raises  the  piece  of  iron  to  the  * 
perpendicular,  so,  at  the  side,  the  iron  is  not  directed  toward 
the  centre,  but  stands  oblique  and  sticks  everywhere ;  for  in 
the  iron  ball  the  pole  is  ever  the  point  of  contact  with  the  ter- 
rella's  pole,  and  it  is  not  constant,  as  it  is  in  the  smaller  terrella. 
The  parts  of  the  earth,  as  of  all  magnetic  bodies,  are  in  accord 
and  enjoy  neighborhood  with  each  other:  there  is  in  them  all 
mutual  love,  undying  good-will.  The  weaker  loadstones  are 
refreshed  by  the  stronger  ones,  and  the  less  vigorous  bring  no 
damage  to  the  more  vigorous.  Yet  a  strong  loadstone  exerts 
more  attraction  in  another  strong  one  than  in  one  that  is 
feeble,  for  a  vigorous  stone   contributes  forceful    action,  and 


148  WILLIAM  GILBERT. 

itself  hastes,  flies  to  the  other,  and  solicits  it  vehemently; 
accordingly  there  is  co-operation,  and  a  clearer  and  stronger 
cohesion. 


CHAPTER    XXVI. 

WHY  THE  LOVE  OF  IRON  AND  LOADSTONE  APPEARS  GREATER 
THAN  THAT  OF  LOADSTONE  AND  LOADSTONE,  OR  IRON 
AND  IRON  WHEN  NIGH  A  LOADSTONE  AND  WITHIN  ITS 
FIELD. 

One  loadstone  does  not  attract  another  on  all  its  sides  as 
it  does  iron,  but  only  at  one  fixed  point :  hence  the  poles  of 
the  two  must  be  properly  arranged,  else  they  do  not  duly  and 
powerfully  cohere.  But  this  arranging  is  not  easy  nor  the 
work  of  an  instant :  therefore  one  loadstone  will  seem  to  be 
refractory  toward  another,  whereas  they  may  be  in  perfect  har- 
mony. Iron,  suddenly  impressed  by  a  loadstone,  is  not  only 
attracted  by  it,  but  is  renovated  and  its  powers  enhanced, 
whereby  it  pursues  and  solicits  the  loadstone  with  a  force  not 
less  than  its  own,  and  also  makes  captive  other  iron  objects. 
Suppose  a  little  iron  bar  firmly  adhering  to  a  loadstone :  if 
you  bring  near  this  piece  of  iron  an  iron  rod,  but  without 
touching  the  loadstone,  you  shall  see  the  iron  instantly  follow 
the  rod,  relinquishing  the  loadstone,  leaning  toward  the  rod, 
and,  on  contact,  firmly  adhering  thereto;  for  iron  in  union  and 
contact  pulls  more  vigorously  another  piece  of  iron  within  the 
field  of  a  loadstone  than  does  the  loadstone  itself.  The  natu- 
ral magnetic  force,  which  in  iron  lies  confined  and  asleep,  is 
awakened  by  a  loadstone,  associates  itself  with  it,  and  comes 


LOVE    OF  IRON  AND   LOADSTONE.  I49 

into  sympathy  with  it  in  virtue  of  the  primary  form : '  hence 
comes  the  perfect  magnetized  iron,  which  is  as  strong  as  the 
loadstone  itself ;  for  as  the  one  imparts  and  arouses,  so  the 
other  conceives,  and,  being  awakened,  endures,  and  by  its  very 
act  gives  back  the  force  again.  But  in  so  much  as  iron  is 
liker  to  iron  than  is  loadstone,  and  in  two  pieces  of  iron  within 
the  field  of  a  loadstone,  the  nighness  of  the  latter  enhances 
the  powers  of  both:  then,  their  forces  being  equal,  likeness  of 
substance  becomes  decisive,  and  iron  gives  itself  up  to  iron, 
and  the  two  pieces  are  united  by  their  most  like  (identical) 
and  homogeneous  forces.  This  is  effected  not  only  by  coition, 
but  by  a  firmer  union  ;  and  a  steel  cap  or  snout  {glans  vel 
nasus)  properly  adjusted  to  the  pole  of  a  loadstone  lifts  greater 
weights  than  can  the  stone  by  itself.  When  steel  or  iron  is 
made  from  loadstone  or  from  iron  ore,  the  slag  and  impuri- 
ties are  separated  from  the  substance  by  a  better  fusion  :  hence 
usually  such  iron  contains  the  matter  of  the  earth  purged  of 
foreign  admixture  and  dross,  and  more  homogenic  and  perfect 
(than  before  smelting),  albeit  deformed  by  fusion.  And  this 
matter,  when  acted  on  by  a  loadstone,  conceives  the  magnetic 
virtue,  and  within  the  magnetic  field  is  endowed  with  force 
surpassing  that  of  an  inferior  loadstone,  which  is  seldom  with- 
out some  admixture  of  impurities. 

*  "  Let  us  imagine  that  that  which  impels  the  iron  towards  the  loadstone, 
or  the  loadstone  towards  the  iron,  is  a  third  body,  or  rather  a  certain  matter 
which  is  in  motion,  and  which  is  very  subtle,  because  it  cannot  be  perceived  by 
our  senses."  {]&cohi  KohaxilxX,  Fhysica,  1718,  Par.  Ill,  Cap.  VIII,  page  391, 
or  Dr.  Clarke's  translation,  1728,  Vol,  II,  page  167.) 


ISO 


WILLIAM  GILBERT, 


CHAPTER  XXVII. 

*THAT  THE  CENTRE  OF  THE  MAGNETIC  FORCES  IN  THE 
EARTH  IS  THE  CENTRE  OF  THE  EARTH;  AND  IN  THE 
TERRELLA  THE  TERRELLA'S  CENTRE. 

The  rays  of  magnetic  force  are  dispersed  in  a  circle  in  all 
directions ;  and  the  centre  of  this  sphere  is  not  in  the  pole  (as 
Baptista  Porta  deems,  Chap.  XXII),  but  in  the  centre  of  the 
stone  and  of  the  terrella.  So,  too,  the  earth's  centre  is  the  centre 
of  the  earth's  magnetic  movements,  though  magnetic  bodies  are 
not  borne  direct  toward  the  centre  in  the  magnetic  movement 
save  when  they  are  attracted  by  the  pole.  For  as  the  formal 
power  of  loadstone  and  earth  promotes  simply  unity  and  con- 
formity between  things  separate,  it  follows  that  everywhere  at 
equal  distance  from  the  centre  or  from  the  convex  circum- 


ference, just  as  at  one  point  it  seems  to  attract  in  a  right  line,  so 
at  another  it  can  control  and  rotate  the  needle,  provided  only 
the  loadstone  be  not  of  unequal  power.     For  if  at  the  distance 


LOADSTONE  DOES  NOT  ATTRACT    TO  A    FIXED  POINT.    I5I 

C  from  pole  D  the  stone  is  able  to  attract  the  needle,  then  at 
an  equal  distance  A  above  its  equator  it  can  control  and  rotate 
the  needle.  Thus  the  centre  and  middle  of  the  terrella  is  the 
centre  of  force,  and  thence  to  the  circumference  of  its  sphere 
of  influence  its  magnetic  virtues  extend  (for)  equal  distances 
in  all  directions. 


CHAPTER   XXVIII. 

THAT  A  LOADSTONE  DOES  NOT  ATTRACT  TO  A  FIXED  POINT 
OR  POLE  ONLY,  BUT  TO  EVERY  PART  OF  A  TERRELLA, 
EXCEPT  THE  EQUINOCTIAL  CIRCLE. 

Coition  is  always  strongest  when  pole  touches  pole,  for  at 
the  poles  the  force  is  greatest  by  concert  of  the  whole :  hence 
one  pole  seizes  the  other  with  greatest  force.  Points  at  dis- 
tances from  the  poles  possess  attractional  power  also,  but 
somewhat  weaker  and  sluggish  in  the  ratio  of  the  distance,  so 
that  finally  in  the  equinoctial  line  they  are  utterly  enervate 
and  faint.  The  poles,  too,  do  not  attract  as  mathematical 
points,  nor  does  magnetized  iron  unite  at  its  poles  only  with 
the  poles  of  a  loadstone.  On  the  contrary,  the  coition  takes 
place  all  over  the  periphery,  north  and  south,  the  force  ema- 
nating from  the  whole  mass.  Magnetic  bodies,  however,  are 
attracted  feebly  in  the  parts  near  the  equator,  but  quickly  in 
the  parts  near  the  poles.  Wherefore  not  the  poles  alone,  and 
not  the  parts  alone  that  are  near  the  poles,  attract  and  solicit 
magnetic  bodies ;  but  magnetic  bodies  are  controlled  and  rotated 
and  unite  with  other  magnetic  bodies  according  as  parts  neigh- 
boring and  adjoining  lend  their  forces,  which  forces  are  ever  of 
the  same  potency  in  the  same  parallel,  except  when  otherwise 
distributed  by  causes  producing  variation. 


152  WILLIAM  GILBERT. 


CHAPTER   XXIX. 

OF  DIFFERENCE    OF    FORCES    DEPENDENT    ON    QUANTITY   OR 

MASS. 

Loadstones  coming  from  the  same  mine,  and  not  inter- 
mingled with  neighboring  metals  or  ores,  have  the  same 
potency ;  yet  the  stone  that  is  largest  exhibits  greatest  force, 
as  it  carries  the  greatest  weight  and  has  a  wider  sphere  of  influ- 
ence. A  loadstone  weighing  an  ounce  does  not  lift  an  iron 
spike  as  does  one  that  weighs  a  pound,  nor  does  its  control 
reach  so  far,  nor  does  its  force  extend  to  such  a  distance. 
And  if  you  take  from  a  one-pound  stone  a  part,  somewhat  of 
its  power  will  be  seen  to  leave  also ;  for  when  a  part  is  taken 

*away  some  of  the  energy  is  lost.  But  when  such  part  is  duly 
applied  and  united  to  the  stone,  though  it  be  not  cemented 
there  nor  perfectly  fitted  in  by  the  mere  apposition,  the  origi- 
nal strength  is  recovered,  and  the  force  returns.     Sometimes, 

♦however,  the  energy  is  increased  by  detachment  of  a  part 
because  of  malformation  of  the  stone,  as  when  the  force  is 
diffused  through  awkward  corners. 

In  stones  of  different  sorts  the  ratio  of  power  is  different : 
one  weighing  a  drachm  may  have  more  force  than  another  one 
of  20  pounds.  Many  a  loadstone  is  so  weak  that  the  force  can 
scarcely  be  noticed,  and  such  faint  magnets  are  often  surpassed 
by  masses  prepared  of  potter's  earth.  But  we  may  ask :  Sup- 
posing that  a  stone  of  a  given  kind  and  of  definite  goodness, 
and  weighing  a  drachm,  carries  one  drachm,  whether  one 
weighing  an  ounce  will  carry  an  ounce,  a  pound  a  pound,  and 

*so  on  ?  So  it  is,  for  in  proportion  to  size  such  loadstone  has 
greater  or  less  strength :  so  that  a  loadstone  of  proportionate 


SHAPE  AND  MASS  ARE  IMPORTANT.  1 53 

size  and  weight,  a  drachm  weight  of  which  lifts  a  drachm 
weight  of  iron,  will,  when  brought  near  a  suitable  great  obelisk 
or  enormous  pyramid  of  iron,  attract  it  and  pull  it  to  itself, 
and  that  with  no  greater  effort  of  its  nature  and  with  no 
greater  pains  than  when  a  drachm  weight  of  loadstone  seizes 
a  drachm  weight  of  iron.  But  in  all  such,  experiments  the 
power  of  the  loadstones  should  be  equal,  the  form  of  the 
stones  should  be  exactly  proportioned  :  this  is  true  not  less  of 
an  armed  than  of  a  naked  loadstone.  As  an  experiment,  take 
a  loadstone  weighing  8  oz.,  which  when  armed  lifts  12  oz.  of* 
iron ;  cut  off  of  this  stone  a  part  which,  when  brought  to  the 
form  of  the  whole  stone  as  it  was  before,  shall  weigh  only 
2  oz. :  such  a  stone,  armed,  lifts  3  oz.  of  iron.  In  this  experi- 
ment it  is  requisite  that  the  form  of  the  3-oz.  piece  of  iron  be 
the  same  as  that  of  the  12-oz.  piece  ;  if  the  12  oz.  mass  rose  in 
form  of  a  cone,  the  3-oz.  piece  must  assume  a  pyramidal  form 
proportioned  to  the  figure  of  the  original  mass. 


CHAPTER  XXX. 

THE  SHAPE  AND  THE  MASS    OF    AN    IRON    OBJECT    ARE    IM- 
PORTANT  IN   MAGNETIC   COITIONS. 

It  was  shown  before  that  the  shape  and  mass  of  a  loadstone 
are  weighty  factors  in  magnetic  coitions  :  similarly,  the  shape 
and  mass  of  the  iron  determine  whether  its  force  shall  be  great 
or  little.  Oblong,  bacilliform  pieces  are  both  more  quickly  at- 
tracted and  cling  more  firmly  than  spherical  or  square  pieces,  and 
this  for  the  causes  we  have  shown  with  regard  to  the  loadstone. 
It  is  also  worthy  of  note,  that  when  a  smaller  iron  object  has  at- 


154  WILLIAM  GILBERT 

tached  to  it  a  weight  of  different  material,  so  that  the  weight 
*of  the  two  shall  equal  that  of  another  larger  piece  whose 
weight  is  proportioned  to  the  power  of  the  loadstone,  it  is  not 
lifted  by  the  loadstone  like  the  larger  object ;  for  the  smaller 
piece  is  not  so  powerfully  attracted  by  the  loadstone,  because 
it  gives  back  less  force,  and  only  magnetic  matter  conceives 
the  magnetic  energy :  foreign  matter  appended  to  such  a  body 
cannot  take  in  magnetic  force. 


CHAPTER  XXXI. 

OF  OBLONG  AND   ROUND     STONES. 

Iron  bodies  are  more  forcibly  attracted  by  an  oblong  stone 
than  by  a  round  one,  provided  only  the  pole  of  the  stone  is  at 
the  extreme  end  of  its  length.  The  reason  is  that  in  the 
oblong  stone  the  magnetic  body  at  the  extremity  is  directed 
straight  toward  a  body  wherein  the  force  proceeds  in  right 
lines  and  through  a  longer  diameter.  But  the  oblong  stone 
has  only  little  force  on  the  side ;  for,  plainly,  the  attraction  at 
a  and  B  is  stronger  in  a  round  loadstone  at  equal  distance 
*  from  the  pole,  than  in  c  and  D. 


PROBLEMS  AND   MAGNETIC  EXPERIMENTS.  155 


CHAPTER   XXXII. 

SOME  PROBLEMS  AND  MAGNETIC  EXPERIMENTS  ON  THE  CO- 
ITION, AND  REPULSION,  AND  REGULAR  MOVEMENT,  OF 
MAGNETIC   BODIES. 

Loadstones    that   are  equal   come    together   with    equal* 
mutual  incitation. 

Magnetized  iron  bodies  that  are  in  all  respects  equal  do  * 
also  come  together  with  equal  mutual  incitation. 

Iron   bodies  not    magnetized,  if  they  are  equal,  and   not* 
hindered    by  their  bulk,  do  also  come  together  with   equal 
movement. 

Two  loadstones  placed  on  suitable  floats  apart  on  the  sur- 
face of  water,  if  they  be  suitably  arranged  within  their  mag- 
netic field,  attract  each  other.  So,  too,  a  proportionate  piece 
of  iron  on  one  float  hastes  to  a  loadstone  with  the  same  speed 
with  which  the  magnet  itself,  afloat,  strives  to  reach  the  iron. 
For  the  two  are  impelled  from  their  own  places  on  either  side 
to  come  together  midway  and  coalesce.  Two  magnetized-iron* 
wires,  floated  in  water  by  suitable  corks,  move  forward  to  con- 
tact, and,  with  the  proper  end  on,  strike  and  are  joined. 

With  magnetic  bodies  that  are  equal,  coition  is  more  vigor-* 
ous,  and  quicker  than  repulsion  and  separation.  That  mag- 
netic bodies  are  more  sluggish  in  repelling  than  in  attracting, 
is  seen  in  every  magnetic  experiment,  as  when  loadstones  are 
borne  on  suitable  floats  on  water,  or  when  magnetized  iron 
wire  or  little  bars  are  driven  through  cork  and  set  afloat  in 
water,  as  also  in  experiments  with  a  needle.  The  reason  is 
that,  since  the  power  of  coition  is  one  thing,  the  power  of  con- 


156 


WILLIAM  GILBERT. 


formation  and  of  ordering  in  place  is  another,  therefore  repul- 
sion and  aversation  are  the  act  of  the  force  ordering  in  place ; 
but  the  coming  together  is  the  result  of  mutual  attraction  to 
contact  as  well  as  of  the  force  that  orders  in  place  ;  i.e.,  it  is 
due  to  a  twofold  force. 

The  ordering  force  is  often  only  the  forerunner  of  coition, 
so  that  the  bodies  shall  stand  in  due  position  before  the  onset : 
hence  they  turn  in  the  direction  of  the  points  of  coition,  if  they 
be  hindered  from  attaining  those  points.     If  a  loadstone  be 


*cut  in  two  equal  parts  along  the  meridian,  the  separated  parts 
repel  each  other,  if  the  poles  be  placed  at  a  suitable  even  dis- 
tance from  each  other  ;  for  they  mutually  repel  with  greater 
velocity  than  is  the  case  when  pole  is  wrongly  opposed  to  pole. 
Thus  the  half  B  oi  a  loadstone,  placed  near  the  other  half  A, 
repels  A  on  its  float,  because  D  withdraws  from  F  and  E  from 
C.  But  if  B  be  again  joined  exactly  with  A,  they  come  to- 
gether and  form  one  magnetic  body ;  yet  when  they  are  only 
near  each  other  they  are  mutually  hostile.  And  if  one  half  be 
turned  about  so  as  to  bring  C  opposite  to  D  and  F  to  E,  then 
A  follows  B  within  the  field  and  becomes  joined  to  it. 


PROBLEMS  AND  MAGNETIC  EXPERIMENTS.  1 5/ 

South  parts  of  a  stone  retreat  from  south  parts,  and  north 
parts  from  north.  Nevertheless,  if  you  bring  the  south  end  of 
a  piece  of  iron  near  to  the  south  part  of  the  stone,  the  iron  is 
seized  and  the  two  are  held  in  friendly  embrace  ;  as  the  ver- 
ticity  fixed  in  the  iron  is  reversed  and  changed  by  the  presence 
of  the  more  powerful  loadstone,  which  is  more  constant  in  its 
forces  than  the  iron.  For  they  come  together  in  accordance 
with  nature,  if  either  by  reversal  or  change  there  be  produced 
true  conformity  and  orderly  coition  as  well  as  regular  direction. 
Loadstones  of  identical  shape,  size,  and  strength  attract  each 
other  with  equal  force,  and  when  in  wrong  position  repel  with 
like  energy. 

Little  rods  of  unmagnetized  iron,  though  like  and  equal,* 
yet  act  on  one  another  often  with  different  force  ;  for  as  there 
are  different  grounds  for  the  acquisition  of  verticity  and  also 
of  strength  and  vigor,  so  the  particles  that  are  most  strongly 
excited  by  the  loadstones  themselves  in  turn  act  with  most 
force. 

Pieces  of  iron  that  have  been  magnetized  at  one  same  pole* 
of  a  loadstone  repel  one  another  at  the  magnetized  ends ;  and 
their  other  extremities  are  also  mutually  hostile. 

In  rotating  needles  when  the  points  are  magnetized  but* 
not  the  crotches,  the  latter  repel  one  another,  but  only  feebly 
and  in  proportion  to  length. 

In  like  rotating  needles  when  the  points  are  magnetized  by* 
the  same  pole  of  a  loadstone  the  crotches  attract  with  equal 
force. 

In  a  long  rotating  needle  the  crotch  is  attracted  feebly  by* 
the  point  of  a  short  needle ;    the  crotch  of  a  short  one  is 
attracted   strongly  by  the  point  of  a  long  one,  because  the 
crotch  of  a  long  needle  has  feeble  verticity,  but  the  point  of  a 
long  needle  has  strong  verticity. 


158  WILLIAM  GILBERT. 

*  The  point  of  a  long  needle  repels  the  point  of  a  short  one 
more  strongly  than  the  point  of  a  short  needle  repels  that  of  a 
long  one,  if  one  of  them  be  poised  free  on  a  sharp  point  and 
the  other  held  in  the  hand ;  for  though  both  have  been 
equally  magnetized  by  the  same  loadstone,  still  the  longer 
one,  by  reason  of  its  greater  mass,  has  greater  force  at  its 
point. 

*  In  unmagnetized  iron  rods  the  south  end  of  one  attracts 
the  north  end  of  another,  and  the  north  end  the  south; 
the  meridional  parts,  too,  repel  meridional  parts,  and  north 
parts  north  parts. 

If  magnetic  bodies  be  divided  or  in  any  way  broken  up, 
each  several  part  hath  a  north  end  and  a  south  end. 

*  A  needle  is  stirred  by  a  loadstone  at  as  great  a  distance 
with  an  obstacle  interposed  as  in  air  and  in  an  open  medium. 

*  Rods  magnetized  by  friction  with  the  pole  of  a  loadstone 
draw  toward  that  pole  and  follow  it.  Baptista  Porta  is  there- 
fore in  error  when  he  says  (Chapter  IV)  that  "if  you  bring  a 
part  nigh  the  part  that  gave  it  the  force,  it  shudders,  and 
repels  and  drives  it  away,  and  attracts  the  converse  and  oppo- 
site part." 

The  laws  of  rotation  and  attraction  are  the  same  as  be- 
tween loadstone  and  loadstone,  loadstone  and  iron,  and  iron 
and  iron. 

When  the  parts  of  a  magnetic  body  that  has  been  broken 
up  by  force  and  cut  into  pieces  are  put  together  again  and 
properly  joined,  they  form  one  body  and  their  joint  force  is 
one ;  nor  have  they  separate  poles. 

*  The  separated  parts,  if  division  has  not  been  made  on  the 
'  parallels,  assume  new  poles,  north  and  south  ;  if  the  division  is 

along  a  parallel,  they  may  retain  one  pole  in  the  same  place  as 
before. 


PROBLEMS  AND   MAGNETIC  EXPERIMENTS. 


159 


Iron  rubbed  and  excited  by  a  loadstone  is  seized  at  the 
fitting  ends  by  a  loadstone  more  powerfully  than  iron  not 
magnetized. 

If  a  small  iron  bar  be  set  erect  on  the  pole  of  a  loadstone,* 
another  bar-iron    pin    in    touch  with   its   upper  end  becomes 
firmly  attached  thereto,  and  if  it   be   moved   away  pulls  the 
standing  bar  from  the  terrella. 

If,  to  the  nether  end  of  the  erect  bar  you  apply  the  end  of* 
another  bar,  it  does  not  cohere,  nor  do  they  unite. 

As  a  rod  of  iron  pulls  iron  away  from  the  terrella,  so  does 
a  small  loadstone  or  a  smaller  terrella    albeit  of  less  force. 


Here  the  iron  bar  C  coalesces  with  the  terrella  A,  and  thus  its 
force  is  enhanced  and  awakened  magnetically  both  in  the  end 
in  conjunction  and  also  in  the  distal  end  by  reason  of  its  con- 
tact with  the  terrella ;  the  distal  end  furthermore  receives 
energy  from  the  loadstone  B,  and  the  pole  D  of  this  magnet 
also  gains  force  by  reason  of  its  favorable  position  and  the 
nearness  of  the  pole  E  of  the  terrella.  Hence  many  causes 
cooperate  to  make  the  bar   C,  attached  to  the  loadstone  B, 


l6o  WILLIAM  GILBERT. 

cling  more  strongly  to  that  than  to  the  terrella  A.  The 
energy  called  forth  in  the  bar,  also  the  energy  called  forth  in 
the  loadstone  j5,  and  B's  native  energy,  all  concur;  therefore 
D  is  magnetically  bound  more  strongly  to  C  than  E  to  C. 

But  if  you  turn  the  pole  F  to  the  iron  C,  then  C  does  not 
cling  to  F  as  it  did  before  to  D ;  for,  within  the  magnetic 
field,  stones  so  arranged  stand  in  an  unnatural  order:  hence  F 
does  not  get  force  from  E. 

„  Two  loadstones,  or  two  magnetized  pieces  of  iron,  duly 
cohering,  fly  apart  on  the  coming  of  a  stronger  loadstone  or  a 
stronger  magnetized  mass  of  iron  ;  for  the  newcomer,  present- 
ing the  opposite  pole,  puts  one  to  flight  and  overmasters  it, 
and  the  mutual  action  of  the  two  that  before  were  conjoined 
ceases.  So  the  forces  of  one  of  the  bodies  are  reduced  and 
fail ;  and  were  it  possible,  it  would  shake  off  its  fellow,  and, 
turning  about,  would  go  rolling  over  to  the  stronger.  For  this 
reason  it  is  that  magnetic  bodies  held  pendent  in  air  drop  to 
the  ground  when  the  opposite  pole  of  a  loadstone  is  presented 
to  them;  and  this  not  because  there  is  any  weakening  or 
numbing  of  the  forces  of  both  of  the  bodies  before  conjoined,  as 
Baptista  Porta  maintains,  for  pole  cannot  be  hostile  to  both  of 
the  ends  that  cohere,  but  to  one  only:  this  end  the  newcomer, 
the  stronger  loadstone,  drives  away  from  itself  by  presenting 
its  opposite  pole,  and  thus  one  of  the  smaller  bodies  is  com- 
pelled to  give  up  its  friendly  association  with  the  other. 


STRENGTH  AND  MOVEMENT  OF  COITION.  l6l 


CHAPTER   XXXIII. 

OF  THE  DIFFERENCE  IN  THE  RATIO  OF  STRENGTH  AND 
MOVEMENT  OF  COITION  WITHIN  THE  SPHERE  OF  IN- 
FLUENCE. 

If  the  greatest  weight  that  is  attracted  to  a  loadstone  at 
the  nearest  distance  be  divided  into  a  given  number  of  parts, 
and  the  radius  of  the  sphere  of  magnetic  attraction  into  the 
same  number  of  parts,  the  parts  of  the  weight  will  correspond 
to  the  intermediate  parts  of  the  radius. 

The  sphere  of  influence  extends  farther  than  the  sphere  of 
movement  of  any  magnetic  body,  for  a  magnetic  body  is 
affected  at  the  outermost  edge  though  it  may  not  move  with 
local  motion :  that  is  done  when  the  loadstone  is  brought 
nearer.  A  needle,  even  a  very  small  one,  turns  round  while 
remote  from  a  loadstone,  though,  at  the  same  distance  and  free 
to  move  and  in  no  wise  hindered,  it  does  not  come  to  the 
loadstone. 

The  velocity  of  the  movement  of  a  magnetic  body  to  a 
loadstone  is  in  proportion  to  the  strength  of  the  loadstone,  or 
its  mass,  or  its  shape,  or  the  nature  of  the  medium,  or  the  dis- 
tance within  the  magnetic  sphere  of  action. 

A  magnetic  body  approaches  with  greater  velocity  a* 
powerful  loadstone  than  a  sluggish  one,  in  the  ratio  of  the 
respective  energies  of  the  two  loadstones.  A  smaller  mass  of 
iron,  as  also  one  rather  oblong  in  shape,  is  attracted  with  the 
greater  velocity.  The  velocity  of  the  movement  of  a  mag- 
netic body  to  a  loadstone  varies  according  to  the  medium,  for 


l62  WILLIAM   GILBERT. 

bodies  move  with  greater  velocity  in  air  than  in  water,  and  in 
a  serene  atmosphere  than  in  thick  and  foggy  weather. 

In  the  ratio  of  distance,  movement  is  quicker  from  anear 
than  from  afar.  At  the  outermost  edge  of  a  terrella's  field 
magnetic  bodies  move  faintly  and  slowly.  In  the  immediate 
neighborhood  of  the  terrella  the  motor  impetus  is  greatest. 
,  A  loadstone  that  in  the  outermost  verge  of  its  field  of 
force,  at  the  distance  of  one  foot,  can  hardly  stir  a  rotating 
needle,  will,  when  connected  with  a  long  iron  rod,  strongly 
attract  and  repel  (accordingly  as  its  different  poles  are  pre- 
sented) the  needle  at  the  distance  of  three  feet,  and  this 
whether  the  loadstone  is  armed  or  unarmed.  The  iron  rod 
should  be  of  fitting  quality,  and  of  the  thickness  of  the  little 
finger. 

For  the  energy  of  the  loadstone  awakens  verticity  in  the 
iron  and  passes  in  and  through  iron  to  a  far  greater  distance 
than  it  extends  through  air. 

The  force  also  passes  through  a  number  of  pieces  of  iron 
conjoined  at  their  extremities,  yet  not  so  surely  as  through 
one  continuous  rod. 

Steel-filings  strewed  on  paper  rise  on  end  and  present  the 
appearance  of  stubby  steel  hairs  when  a  loadstone  is  brought 
near  above  them  ;  when  the  loadstone  is  appHed  beneath,  the 
hairlike  crop  rises  also. 

,  Steel-filings,  when  the  pole  of  a  loadstone  is  brought  near, 
coalesce  into  one  body  ;  but  when  it  would  come  to  the  load- 
stone, the  body  is  broken  up  and  rises  to  the  steel  in  smaller 
masses  that  still  hold  together. 

But  if  the  loadstone  be  beneath  the  paper,  the  consolidated 
mass  breaks  up  as  before,  and  into  very  many  parts,  each  of 
which  consists  of  a  multitude  of  grains ;  and  they  remain 
united,  like  separate  bodies  ;  and  while  the  lowermost  parts  of 


ivjuy  a  loadstone  is  of  different  power.     163 

these  eagerly  follow  the  pole  of  the  loadstone  beneath,  so  the 
separate  masses  stand  like  solid  magnetic  bodies.  In  like 
manner  a  bit  of  iron  wire  one  barley-corn  or  two  in  length 
stands  on  end  when  a  loadstone  is  applied  either  beneath  or 
above. 


CHAPTER  XXXIV. 

WHY  A  LOADSTONE  IS     OF  DIFFERENT   POWER   IN  ITS   POLES 
AS   WELL  IN   THE   NORTH   AS   IN   THE   SOUTH   REGIONS. 

The  extraordinary  magnetic  energy  of  the  earth  is  beauti-* 
fully  shown  in  the  following  neat  experiment :  Take  a  terrella 
of  no  ordinary  power,  or  an  oblong  loadstone  with  equal  cones 
forming  its  polar  ends  ;  but  in  any  figure  not  exactly  spheri- 
cal it  is  easy  to  fall  into  mistakes,  and  the  experiment  is  diffi- 
cult. In  northern  latitudes  raise  the  true  north  pole  above 
the  horizon  straight  toward  the  zenith.  Plainly  it  holds  erect 
on  its  north  pole  a  larger  bar  of  iron  than  could  the  south 
pole  of  the  same  terrella  if  turned  in  like  manner  toward  the 
centre  of  the  sky.  The  same  demonstration  is  made  with  a 
small  terrella  set  atop  of  a  large  one. 

Let  ab  be  the  earth  or  a  large  terrella,  and  ab  a  small  ter- 
rella; a  larger  bar  is  raised  erect  by  the  north  pole  of  the 
small  terrella  than  the  b  pole  of  the  same,  if  turned  skyward, 
can  raise  to  the  erect  position.  And  the  a  pole  of  the  small 
terrella  derives  force  from  the  greater,  turning  from  zenith  to  * 
the  plane  of  the  horizon  or  to  the  level.  Now  if,  the  smaller 
terrella  having  its  poles  directed  as  before,  you  apply  a  piece 


1 64 


WILLIAM  GILBERT. 


of  iron  to  its  lower  or  south  pole,  that  will  attract  and  hold  a 
greater  weight  than  can  the  south  pole  if  that  be  turned  down. 
Which  is  thus  shown  :  Let  A  be  the  earth  or  a  terrella  ;  E  the 


north  pole  or  some  point  in  high  latitude  ;  let  ^  be  a  large 
terrella  above  the  earth,  or  a  small  terrella  above  a  larger  one ; 
D  the  south  pole :  it  is  plain  that  D  (south  pole)  attracts  a 
larger  piece  of  iron,  C,  than  can  E  (the  north  pole),  if  that  pole 
be  turned  downward  to  the  position  D,  looking  toward  the 
earth  or  the  terrella  in  their  northern  regions.  Magnetic 
bodies  gain  force  from  other  magnetic  bodies  if  they  be  ar- 
ranged duly  and  according  to  their  nature  in  neighborhood 
and  within  the  sphere  of  influence  ;  and  hence,  when  a  terrelld 
is  imposed  on  the  earth  or  on  another  terrella  in  such  way 
that  the  south  pole  looks  toward  the  north  pole,  and  north  is 
turned  away  from  north,  the  energy  and  forces  of  its  poles  are 
augmented.  Hence  the  north  pole  of  a  terrella  in  such  posi- 
tion lifts  a  heavier  piece  of  iron  than  the  south  pole  does  if  that 
be  turned  away.     In  like  manner  the  south  pole,  gaining  force 


fVJ/y  A   LOADSTONE  IS  OF  DIFFERENT  POWER.       165 

from  the  earth  or  the  larger  terrella  when  it  is  duly  placed  as 

nature  requires,  attracts  and  holds  heavier  bars  of  iron.     In  * 

he  other  portion  of  the  terrestrial  globe,  toward  the  south,  as 


also  in  the  southern  parts  of  the  terrella,  the  case  is  reversed, 
for,  there,  the  south  pole  of  the  terrella  is  strongest  when  distal, 
as  is  the  north  pole  of  the  terrella  when  it  faces  the  earth 
or  terrella.  The  farther  a  place  is  from  the  equinoctial  line, 
whether  of  the  earth  or  of  a  terrella,  the  greater  is  seen  to  be 
the  accession  of  force ;  but  nigh  the  equator  the  difference  is 
slight ;  at  the  equator  it  is  null ;  at  the  poles  it  is  greatest. 


l66  WILLIAM  GILBERT. 


CHAPTER  XXXV. 

OF    A    PERPETUAL-MOTION    ENGINE    ACTUATED    BY    THE    AT- 
TRACTION  OF  A   LOADSTONE,  MENTIONED   BY  AUTHORS. 

Cardan  writes  that  out  of  iron  and  loadstone  may  be  con- 
structed a  perpetual-motion  engine — not  that  he  saw  such  a 
machine  ever ;  he  merely  offers  the  idea  as  an  opinion,  and 
quotes  from  the  report  of  Antonius  de  Fantis,  of  Treviso ; 
such  a  machine  he  describes  in  Book  IX,  De  Rerum  Varietate. 
But  the  contrivers  of  such  machines  have  but  little  practice  in 
magnetic  experiments.  For  no  magnetic  attraction  can  be 
greater  (whatever  art,  whatever  form  of  instrument  you  em- 
ploy) than  the  force  of  retention  ;  and  objects  that  are  con- 
joined, and  that  are  near,  are  held  with  greater  force  than 
objects  solicited  and  set  in  motion  are  made  to  move ;  and  as 
we  have  already  shown,  this  motion  is  a  coition  of  both,  not 
an  attraction  of  one.  Such  an  engine  Petrus  Peregrinus,  cen- 
turies ago,  either  devised  or  delineated  after  he  had  got  the 
idea  from  others ;  and  Joannes  Taysner  published  this,  illus- 
trating it  with  wretched  figures,  and  copying  word  for  word 
the  theory  of  it.  May  the  gods  damn  all  such  sham,  pilfered, 
distorted  works,  which  do  but  muddle  the  minds  of  students !  * 

'  See  note  2,  page  9,  relative  to  Joannes  Taisnier  Hannonius. 

With  reference  to  the  above-named  passage,  P.  D.  Timoteo  Bertelli  Barna- 
bita,  at  Chap.  VI,  page  22,  of  his  Memoir  on  P.  Peregrinus,  says  that  Gilbert 
has  "appropriated  other  observations  and  experiments  of  Peregrinus,"  and  has 
taken  from  him  the  idea  of  his  ierrella  as  well  as  the  experiments  on  magnetic 
polarity.  Farther  on  (page  28)  Bertelli  gives  the  following  extract  from  Theve- 
not ;  "  5°  L'on  voit  encore  que  la  pluspart  des  choses  que  Ton  attribue  ^  Gilbert 
et  que  luy  ont  donn6  la  reputation  de   Fere  de  la  Philosophic  de  I'Ayman 


HOW  A    STRONG  LOADSTONE  MAY  BE  RECOGNIZED.     167 


CHAPTER  XXXVI. 

HOW  A   STRONG  LOADSTONE   MAY  BE   RECOGNIZED. 

A  STRONG  loadstone  sometimes  lifts  in  air  a  mass  of  iron 
weighing  as  much  as  itself ;  a  weak  loadstone  hardly  attracts  a 
bit  of  fine  wire.  Those,  then,  are  the  stronger  loadstones 
which  attract  and  hold  the  larger  bodies,  unless  there  is  some 
defect  of  shape,  or  unless  the  pole  of  the  stone  is  not  properly 
appHed.  Besides,  the  stronger  loadstone,  when  afloat,  more 
readily  turns  its  poles  toward  the  poles  of  the  earth  or  the 
points  of  variation  on  the  horizon.  But  the  stone  that  acts 
sluggishly,  betrays  some  flaw  in  itself,  shows  that  its  force  is 
exhausted.  Loadstones  are  to  be  all  prepared  in  the  same 
way,  shaped  alike,  and  made  of  the  same  size  ;  for  when  they 
are  unlike  and  unequal,  experiments  are  doubtful.  All  load- 
stones are  tested  for  strength  in  the  same  way,  viz.,  with  a 
versorium  (rotating  needle)  held  at  some  distance  ;  the  stone 
that  at  the  greatest  distance  is  able  to  make  the  needle  go 
round  is  the  best  and  strongest.  Baptista  Porta  also  rightly 
determines  the  power  of  a  loadstone  by  thus  weighing  in  a 

estaient  sciies  dfes  le  treizieme  siecle."  This,  says  he,  is  "doubtless  an  ex- 
aggeration. That  Gilbert  took  from  P.  Peregrinus  his  terrella  and  many  ex- 
cellent scientific  plans  on  magnetism,  the  ideas  of  others  also,  is  probable,  but 
it  is  indubitable  that  much  was  his  own,  and  that,  for  his  time,  his  work  is  a 
v&itable  chef  d'csuvre  of  inductive  and  experimental  method  and  the  most 
finished  treatise  on  magnetism  which  had  up  to  that  time  appeared." 

Consult,  also,  Bertelli,  page  92  ;  Gilbert,  De  Magnete,  Book  VI,  Chap.  IV  ; 
likewise,  W.  Wenckebach,  "Sur  Petrus  Adsigerius  .  .  .,"  Rome  1865,  page  8, 
and  the  work  therein  quoted  "  Universal  Lexicon,"  Leipzig  1741  ;  also  Nicolao 
Cabeo,  Phil.  Magn.,  Ferrara  1629,  P^ge  23. 


I08  WILLIAM  GILBERT, 

balance.  A  piece  of  loadstone  is  put  in  one  scale  and  an  equal 
weight  of  another  substance  in  the  other,  so  that  the  scales 
are  balanced.  Then  some  iron  lying  on  a  board  is  brought 
nigh,  so  that  it  shall  cleave  to  the  loadstone  in  the  scale,  and 
the  two  bodies  cohere  perfectly  at  their  points  of  attraction ; 
into  the  opposite  scale  sand  is  poured  gradually  till  the  scale 
in  which  is  the  loadstone  separates  from  the  iron.  By  weigh- 
ing the  sand  the  force  of  the  loadstone  is  ascertained.  So, 
too,  we  can  make  experiment  and  find  the  stronger  stone  by 
weighing  sand,  if  we  put  in  a  pair  of  scales  loadstones  that 
balance  each  other.  Such  is  an  experiment  given  by  Cardinal 
Cusanus  in  his  Statica,  and  from  him  Porta  would  seem  to 
have  learned  the  one  he  cites.  The  stronger  loadstones  turn 
readily  toward  the  poles  or  the  points  of  variation  ;  so,  too, 
they  propel  their  floats  and  cause  them  and  other  cumbrances, 
as  so  much  wood,  to  wheel  about.  In  an  inclination  or  dip  in- 
strument the  greater  power  of  a  loadstone  is  manifested  and 
there  greater  power  is  requisite.  Hence  loadstones  are 
stronger  the  more  speedily  they  do  their  work,  and  the  more 
rapidly  they  travel  from  side  to  side  and  return,  and  the 
sooner  they  come  to  a  standstill.  Feeble,  exhausted  load- 
stones travel  more  sluggishly,  come  to  a  rest  more  slowly, 
stick  at  the  pole  less  decisively,  and  are  easily  displaced 
therefrom. 


USES  OF   THE  LOADSTONE  AS  IT  AFFECTS  IRON.     169 


CHAPTER   XXXVII. 

USES  OF  THE  LOADSTONE  AS  IT  AFFECTS  IRON. 

By  means  of  magnetic  coition  we  test  an  iron  ore.  The 
ore  is  roasted  in  a  furnace,  is  crushed,  washed,  dried,  and  so  is 
freed  from  foreign  humors.  The  loadstone  being  thrust  among 
the  particles  collected  from  the  bath  attracts  the  iron  dust, 
which  being  removed  by  a  feather  brush  is  caught  in  a  cruci- 
ble ;  again  and  again  the  loadstone  is  dipped  in  and  the  iron 
dust  brushed  into  the  crucible,  till  nothing  remains  that  it  will 
attract.  Then  the  powdered  iron  is  heated  together  with 
halinitro  till  it  is  melted  and  becomes  a  mass  of  iron.  Now  if 
the  loadstone  picks  up  the  iron  dust  readily  and  easily,  we 
deem  the  ore  to  be  rich ;  if  slowly,  the  ore  is  poor ;  if  the  load- 
stone seems  quite  to  reject  it,  the  ore  is  judged  to  have  little 
or  no  iron.  By  the  same  method,  iron  particles  may  be  sepa- 
rated from  particles  of  any  other  metal.  And  many  tricks  are 
played  by  secretly  attracting  bits  of  iron  to  light  bodies,  or 
causing  a  concealed  loadstone  to  attract  the  iron ;  to  persons 
who  know  not  the  cause,  the  movements  of  the  objects  seem 
amazing.  Any  ingenious  workman  may  exhibit  a  great 
number  of  such  tricks  for  sport,  with  the  air  of  one  deaHng  in 
incantations  and  magic. 


I/O  WILLIAM  GILBERT. 


CHAPTER  XXXVIII. 

OF  THE  ATTRACTIONS  OF  OTHER  BODIES. 

Philosophizers  of  the  vulgar  sort  and  mere  copyists  oft 
repeat,  from  others'  memoirs  on  natural  philosophy,  opinions 
and  errors  with  regard  to  the  attractional  force  of  various 
bodies.  They  will  say,  for  example,  that  diamond  attracts  iron 
and  pulls  it  away  from  loadstone  ;  that  loadstones  differ,  some 
attracting  gold,  others  silver,  copper,  lead — yea,  flesh,  water, 
fish.  The  flame  of  sulphur  is  said  to  seek  iron  and  stones ;  so 
is  white  naphtha  said  to  draw  to  itself  fire.  I  have  already  said 
that  inanimate  natural  bodies  in  no  other  wise  attract  or  are 
attracted  on  this  terrestrial  globe,  save  either  magnetically  or 
electrically.  It  is  therefore  not  true  that  there  are  loadstones 
that  attract  gold  or  other  metals  ;  for  a  magnetic  body  attracts 
only  a  magnetic  body.  Fracastorio  tells  of  having  seen  a 
loadstone  attracting  silver.  If  that  were  true,  then  it  must 
necessarily  have  been  because  some  iron  had  been  artificially 
mixed  with  the  silver  and  lay  hidden  therein,  or  because 
nature  had  mixed  iron  with  the  silver  (as  she  does  sometimes, 
though  very  seldom) ;  for  iron  is  now  and  then  mixed  with 
silver  by  nature,  but  silver  with  iron  very  rarely  or  never.  By 
false  coiners  and  by  avaricious  princes,  when  money  is  coined, 
iron  is  mixed  with  silver;  an  instance  of  this  we  have  in 
Anthony's  denarius,  if  what  Pliny  declares  be  true.  So  Car- 
dan (led  into  error,  perhaps,  by  others)  says  there  is  a  certain 
kind  of  loadstone  which  attracts  silver;  and  he  adds  a  very 
silly  test  of  the  thing :     "  If,"  says  he,  "  a  thin  rod  of  silver  be 


OF   THE  ATTRACTIONS  OF  OTHER  BODIES.  I/I 

touched  with  this  and  then  poised  in  equilibrium,  when  it 
comes  to  a  standstill  after  being  whirled,  it  will  point  to  silver 
(especially  a  large  quantity),  though  the  same  be  buried  in  the 
ground  ;  by  this  means  anybody  may  easily  unearth  hidden 
treasures."  He  adds  that  "  the  stone  must  be  of  the  best," 
and  that  he  never  saw  such  stone.  Nor  will  he  or  anybody 
else  ever  see  such  a  stone  or  such  an  experiment.  Cardan 
cites  an  attraction,  improperly  so  called,  of  flesh,  which  is 
altogether  unlike  magnetic  attraction ;  his  magnes  creagus  (or 
flesh-attracting  loadstone,  so  named  because  it  clings  to  the 
lips)  must  be  cast  out  of  the  company  of  loadstones  and  of  the 
whole  family  of  attractional  bodies.  Lemnian  earth,  red 
ochre,  and  sundry  minerals  have  this  action,  but  it  were 
absurd  to  say  that  they  attract.  Cardan  imagines  another 
loadstone,  a  third  species  as  it  were  ;  if  a  needle  be  driven  into 
this,  it  may  be  thrust  into  a  person's  body  afterward  without 
being  felt.  But  what  has  attraction  to  do  with  numbing  of 
sense,  or  what  is  there  in  common  between  stupefaction  and 
the  mind  of  a  philosopher  while  he  discourses  of  attraction  ? 
Many  are  the  stones,  both  of  natural  origin  and  artificially 
compounded,  that  possess  the  power  of  dulling  the  senses. 
The  flame  of  sulphur  is  by  some  said  to  attract  because  that  it 
consumes  certain  metals  by  reason  of  its  penetrating  force. 
So  does  naphtha  attract  flame  because  it  emits  and  exhales  in- 
flammable vapor,  and  hence  is  set  aflame  at  some  distance ; 
even  as  the  smudge  of  a  candle  that  has  just  been  extinguished 
catches  fire  again  from  another  flame ;  for  fire  creeps  to  fire 
through  an  inflammable  medium.  Of  the  sucking-fish  or  re- 
mora  {Echeneis  rejnord),  and  how  it  stays  ships,  philosophers 
have  discoursed  variously.  It  is  their  custom  oft  to  account  with 
their  reasonings  for  this  and  many  other  fables,  before  ascer- 
taining that  the  thing  is  so  in  fact.     Wherefore,  approving  and 


V]2.  WILLIAM   G I  LB  RET. 

indorsing  the  absurdities  of  the  ancients,  they  published  the 
most  blunderous  theories  and  ridiculous  theses — e.g.,  that  there 
are  rocks  having  the  power  of  attraction  and  that  there  the 
remora  dwells ;  and  they  postulate  of  the  necessity  of  I  know 
not  what  vacuum  or  how  produced.  Pliny  and  Julius  Solinus 
tell  of  the  stone  cathochites  and  affirm  that  it  attracts  flesh  and 
holds  one's  hand,  as  loadstone  holds  iron  and  amber  holds 
chaff.  But  that  is  due  solely  to  its  viscosity  and  its  natural 
glutinousness,  for  it  adheres  most  readily  to  a  warm  hand. 
The  sagda,  or  sagdo,  is  a  gem  of  leek-green  color  mentioned  by 
Pliny,  Solinus,  Albertus  Magnus,  and  Euace,  who  themselves 
make  up  or  from  others  copy  the  story  that  this  stone  has  the 
peculiarity  of  attracting  wood.  And  there  are  others  who 
utter  the  nonsense  that  the  wood  attracted  cannot  be  pulled 
off,  but  has  to  be  cut  away ;  while  some  tell  of  a  stone  of  this 
kind  that  clings  as  firmly  to  ships'  bottoms  as  do  the  barnacles 
gathered  on  a  long  voyage.  But  though  a  stone  may  cling  to 
a  surface,  it  does  not  therefore  attract  ;  and  if  it  did  attract, 
surely  it  would  draw  to  itself  chips  and  shavings  electrically. 
A  stone  of  this  sort  was  seen  by  Encelius  in  the  hands  of  a 
certain  seaman ;  a  weak  stone,  it  was,  hardly  able  to  attract 
the  smallest  twigs  ;  and  its  color  was  not  a  true  leek-green. 
Diamond,  carbuncle,  rock-crystal,  and  other  stones  attract 
in  that  way.  I  say  nothing  of  other  fabulous  stones,  of 
pantarbes  whereof  Philostratus  affirms  that  it  attracts  to  itself 
other  stones ;  of  amphitane,  said  to  attract  also  gold.  Pliny, 
in  telling  of  the  discovery  of  glass,  makes  the  loadstone 
attract  glass  as  it  does  iron ;  for  when  in  speaking  of  the  mode 
of  making  glass  he  describes  its  nature,  he  adds  this  concern- 
ing the  loadstone :  "  In  time  the  skill  of  the  workmen,  clear 
sighted  and  resourceful,  was  no  longer  content  with  mixing  in 
natron ;  loadstone  began  to  be  added  because  it  is  believed  to 


OF   THE  ATTRACTIONS  OF  OTHER  BODIES.  1 73 

attract  to  itself  the  liquid  glass  even  as  it  attracts  iron."' 
Georgius  Agricola  asserts  that  "A  portion  of  loadstone  is 
added  to  the  ingredients  of  glass  (sand  and  natron),  because  it 
is  believed  in  our  day  as  in  early  times  that  that  force  (the 
magnetic)  attracts  to  itself  the  molten  glass  even  as  it  attracts 
iron,  that  it  purifies  it  when  attracted,  and  changes  it  from 
green  or  orange-yellow  to  clear  white ;  but  afterward  the  fire 
consumes  the  loadstone."  True  it  is  indeed  that  loadstone  of 
some  kind  (as  the  magnesia  employed  by  glass-makers,  which 
has  no  magnetic  powers)  is  sometimes  introduced  into  and 
mingled  with  the  material  of  glass,  yet  not  because  that  it 
attracts  glass.  But  a  red-hot  loadstone  does  not  attract  iron 
at  all,  nor  is  iron  at  white  heat  attracted  by  loadstone  ;  and 
the  loadstone  is  even  destroyed  by  very  strong  heat  and  loses 
its  power  of  attraction.  Nor  is  this  work  of  purifying  the 
function  of  loadstone  alone  in  the  glass  furnace,  but  also  of 
certain  pyrites  and  of  readily  combustible  iron  ores ;  and  these 
alone  are  used  by  such  of  our  glass-makers  as  make  clear,  fine 
glass.  These  materials  are  mixed  with  sand,  ashes,  and  natron 
(just  as  other  materials  are  mixed  with  metals  when  they  are 
smelted),  so  that,  when  the  contents  of  the  furnace  become 
fluid  glass,  the  well-known  green  and  yellow  color  may  be 
purged  away  by  the  penetrant  heat.  For  no  other  matter 
reaches  such  degree  of  heat  or  endures  fire  for  the  requisite 

*  The  allusion  to  Pliny  is  made  by  J.  B.  Porta:  Natural  Magick,  London 
1658,  Book  VII,  page  216  ;  Magics  Naturalis,  Amstelodami  1664,  Lib.  VII 
Cap.  LVI,  page  331.  Sir  Thomas  Brown  says  {Pseudoloxia  Epidemica,  London 
1658,  Book  II,  page  76):  "True  it  is  that  in  the  making  of  glass  it  hath  been 
in  ancient  practice  to  cast  in  pieces  of  Loadstone  :  conceiving  it  carried  away 
all  ferreous  and  earthy  parts  from  the  pure  and  running  portion  of  glass, 
which  the  Loadstone  would  not  respect ;  and  therefore  if  that  attraction  were 
not  rather  Electrical  than  Magnetical,  it  was  a  wonderous  effect  what  Helmont 
delivereth  concerning  a  glass  wherein  the  Magistery  of  Loadstone  was  prepared; 
which  after  retained  an  attractive  quality." 


174  WILLIAM  GILBERT. 

length  of  time  that  the  material  of  the  glass  may  become 
perfectly  fluid,  and  just  then  is  burnt  up  by  the  strong  fire.  But 
sometimes  it  happens  that  on  account  of  the  magnetic  stone,  or 
magnesia,  or  iron  ore,  or  pyrites,  the  glass  hath  a  dusky  tinge, 
these  substances  being  too  resistant  to  fire  and  hence  not  being 
burnt  up,  or  having  been  introduced  in  too  great  quantity. 
For  this  reason,  glass-makers  procure  the  right  sort  of  stone 
and  carefully  attend  to  the  proportion  of  ingredients  in  the 
mixture.  Thus,  then,  Georgius  Agricola  and  later  writers  are 
badly  led  astray  by  Pliny's  stupid  philosophy  when  they  de- 
clare that  loadstone  is  needed  by  glass-makers  for  its  magnetic 
virtues  and  attractive  force.  And  Scaliger  {De  Subtil,  ad  Car- 
danufn)  strays  far  from  truth  when,  in  treating  of  magnetic 
bodies,  he  speaks  of  diamond  attracting  iron  ;  unless  he  means 
only  that  diamond  electrically  attracts  iron  as  it  does  bits  of 
wood,  straws,  and  other  small  bodies  of  all  kinds.  Fallopius 
thinks  that  quicksilver  attracts  metals  in  virtue  of  an  occult 
property,  just  as  the  loadstone  does  iron,  or  as  amber  attracts 
chaff.  But  there  is  no  attraction  properly  so  called  when 
quicksilver  enters  into  metals.  For  metals  imbibe  quicksilver 
as  clay  does  water,  but  not  unless  the  substances  are  in  con- 
tact ;  for  quicksilver  does  not  draw  to  itself  gold  or  lead  from 
a  distance,  but  remains  fixed  in  its  place. 


MUTUALLY  REPELLANT  BODIES.  1 75 


CHAPTER  XXXIX. 

OF  MUTUALLY   REPELLANT   BODIES. 

Authors  who  have  treated  of  the  forces  of  attracting 
bodies  have  discoursed  of  the  powers  of  repellant  bodies  also  ; 
and  in  particular  those  who  have  classified  objects  in  nature 
according  to  sympathy  and  antipathy.  It  would  seem,  there- 
fore, that  we  must  needs  say  something  about  the  strife  of 
bodies  among  themselves,  lest  widespread  errors,  accepted  by 
all  to  the  ruin  of  true  philosophy,  should  extend  farther.  They 
tell  us  that  as  like  things  attract  for  conservation's  sake,  so 
unlike  things  and  opposites  repel  and  drive  each  other  away, 
as  is  seen  in  the  antiperistasis  (counteraction)  of  many  bodies ; 
but  it  is  most  potent  in  plants  and  animals,  which,  as  they 
attract  things  in  afifinity  and  of  kin,  so  do  put  away  things 
extreme  and  disadvantageous  to  themselves.  But  in  other 
bodies  the  same  reason  does  not  exist  for  their  coming  to- 
gether by  mutual  attraction  when  they  are  separated.  Ani- 
mals take  food  (as  do  all  things  that  live),  bring  it  into  their 
inwards,  absorb  their  nourishment  by  means  of  certain  organs 
(the  vital  principle  acting  and  operating).  Only  things  set 
before  them  and  adjoining  them  do  they  enjoy  through  a 
natural  instinct,  not  things  placed  afar;  herein  there  is  no 
exercise  of  force,  no  movement  on  the  part  of  those  other 
things ;  and  therefore  animals  neither  attract  bodies  nor  repel. 
Water  does  not  repel  oil,  as  some  do  think,  for  oil  floats  on 
water;  nor  does  water  repel  mud,  because  when  mixed  with 
water  it  settles  at  last.     This  is  a  separation  of  bodies  unlike 


176  WILLIAM  GILBERT. 

or  not  perfectly  mixed,  because  of  their  matter ;  but  after  they 
have  been  separated,  they  still  remain  in  conjunction  without 
any  natural  strife.  Thus,  in  the  bottom  of  a  vessel,  muddy 
sediment  rests  quiet,  and  oil  remains  on  the  top  of  water,  nor 
is  it  ordered  away,  A  drop  of  water  remains  whole  on  a  dry 
surface,  nor  is  it  chased  away  by  the  dry.  Wrongly,  therefore, 
do  they  who  discourse  of  these  things  impart  an  antipathy 
— antipathia  (i.e.,  a  power  of  repulsion  through  opposite 
passions) ;  for  neither  is  there  in  them  any  repellant  force,  and 
repulsion  comes  of  action  not  of  passion.  But  these  people 
dearly  love  their  Greek  terms.  The  question  for  us  is  whether 
there  is  any  body  that  drives  another  away  to  a  distance  with- 
out material  impetus,  as  the  loadstone  attracts.  Now  a  load- 
stone does  repel  another  loadstone ;  for  the  pole  of  one  is 
repelled  by  the  pole  of  another  that  does  not  agree  naturally 
with  it  ;  driving  it,  it  makes  it  turn  round  so  that  they  may 
come  together  perfectly  according  to  nature.  But  if  a  weak 
loadstone  floating  freely  in  water  cannot,  on  account  of  obsta- 
cles, readily  turn  about,  then  it  is  repelled  and  driven  farther 
away  by  the  other.  All  electrics  attract  objects  of  every 
kind ;  they  never  repel  or  propel.  What  is  told  of  some 
plants  (e.g.,  of  the  cucumber,  which,  when  oil  is  placed  beneath 
it,  moves  away)  is  a  material  change  from  neighborhood,  not  a 
hidden  sympathy.  But  when  they  show  you  a  candle's  flame 
that  touches  a  cold  solid  (as  iron)  turning  to  one  side,  and  pre- 
tend that  here  is  antipathy,  they  talk  nonsense.  The  reason 
of  this  they  will  see  clearer  than  light  when  we  come  to  treat 
of  heat  and  what  it  is.  As  for  Fracastorio's  belief  that  a 
loadstone  may  be  found  that  shall  repel  iron,  in  virtue  of  some 
principle  latent  in  it  that  is  opposed  to  iron,  it  is  without  any 
foundation. 


BOOK   III. 


CHAPTER  I. 


OF     DIRECTION. 


In  the  loregoing  books  it  has  been  shown  that  a  loadstone 
has  its  poles,  iron  also  poles,  and  rotation,  and  fixed  verticity, 
and  finally  that  loadstone  and  iron  direct  their  poles  toward 
the  poles  of  the  earth.  But  now  we  have  to  set  forth  the 
causes  of  these  things  and  their  wonderful  efficiencies  known 
aforetime  but  not  demonstrated.  Of  these  rotations  all  the 
writers  who  went  before  us  have  given  their  opinions  with  such 
brevity  and  indefiniteness  that,  as  it  would  seem,  no  one  could 
be  persuaded  thereby,  while  the  authors  themselves  could 
hardly  be  contented  with  them.  By  men  of  intelligence,  all 
their  petty  reasonings — as  being  useless,  questionable,  and 
absurd,  and  based  on  no  proofs  or  premises — are  rejected  with 
the  result  that  magnetic  science,  neglected  more  and  more  and 
understood  by  none,  has  been  exiled.     The  true  south  pole,* 

177 


178  WILLIAM  GILBERT. 

and  not  the  north  (as  before  our  time  all  believed),  of  a  load- 
stone placed  on  its  float  in  water  turns  to  the  north ;  the  south 
end  of  a  piece  of  magnetized  and  of  unmagnetized  iron  also 
moves  to  the  north.  An  oblong  piece  of  iron  of  three  or  four 
finger-breadths,  properly  stroked  with  a  loadstone,  quickly 
turns  to  north  and  south.  Therefore  artificers  place  such  a 
bar,  balanced  on  a  point,  in  a  compass-box  or  in  a  sun-dial ;  or 
they  construct  a  versorium  out  of  two  curved  pieces  of  iron 
that  touch  at  their  extremities  so  that  the  movement  may  be 
more  constant ;  thus  is  constructed  the  mariner's  compass,  an 
instrument  beneficial,  salutary,  and  fortunate  for  seamen,  show- 
ing the  way  to  safety  and  to  port.  But  it  is  to  be  understood 
at  the  threshold  of  their  argument,  before  we  proceed  farther, 
that  these  directions  of  loadstone  or  of  iron  are  not  ever  and 
always  toward  the  world's  true  poles,  that  they  do  not  always 
seek  those  fixed  and  definite  points,  nor  rest  on  the  line  of  the 
true  meridian,  but  that  at  places,  more  or  less  far  apart,  they 
commonly  vary  either  to  the  east  or  to  the  west;  sometimes, 
too,  in  certain  regions  of  land  or  sea,  they  point  to  the  true 
poles.  This  discrepance  is  known  as  the  variation  of  the 
needle  and  of  the  loadstone ;  and  as  it  is  produced  by  other 
causes  and  is,  as  it  were,  a  sort  of  perturbation  and  depravation 
of  the  true  direction,  we  propose  to  treat  here  only  of  the  true 
direction  of  the  compass  and  the  magnetic  needle,  which  would 
all  over  the  earth  be  the  same,  toward  the  true  poles  and  in 
the  true  meridian,  were  not  hindrances  and  disturbing  causes 
present  to  prevent :  in  the  book  next  following  we  will  treat  of 
its  variation  and  of  the  cause  of  perturbation. 

They  who  aforetime  wrote  of  the  world  and  of  natural 
philosophy,  in  particular  those  great  elementarian  philosophers 
and  all  their  progeny  and  pupils  down  to  our  day ;  those,  I 
mean,  who  taught  that  the  earth  is  ever  at  rest,  and  is,  as  it 


DIRECTION.  179 

were,  a  dead-weight  planted  in  the  centre  of  the  universe  at 
equal  distance  everywhere  from  the  heavens,  of  simple  uncom- 
plex  matter  possessing  only  the  qualities  of  dryness  and  cold — 
these  philosophers  were  ever  seeking  the  causes  of  things  in 
the  heavens,  in  the  stars,  the  planets ;  in  fire,  air,  water,  and  in 
the  bodies  of  compounds ;  but  never  did  they  recognize  that 
the  terrestrial  globe,  besides  dryness  and  cold,  hath  some 
principal,  efficient,  predominant  potencies  that  give  to  it  firm- 
ness, direction,  and  movement  throughout  its  entire  mass  and 
down  to  its  inmost  depths ;  neither  did  they  make  inquiry 
whether  such  things  were,  and,  for  this  reason,  the  common 
herd  of  philosophizers,  in  search  of  the  causes  of  magnetic 
movements,  called  in  causes  remote  and  far  away.  Martinus 
Cortesius,  who  would  be  content  with  no  cause  whatever  in 
the  universal  world,  dreamt  of  an  attractive  magnetic  point 
beyond  the  heavens,  acting  on  iron.  Petrus  Peregrinus  holds 
that  direction  has  its  rise  at  the  celestial  poles.  Cardan  was 
of  the  opinion  that  the  rotation  of  iron  is  caused  by  the  star 
in  the  tail  of  Ursa  Major.  The  Frenchman  Bessard  thinks 
that  the  magnetic  needle  turns  to  the  pole  of  the  zodiac. 
MarsiHus  Ficinus  will  have  it  that  the  loadstone  follows  its 
Arctic  pole,  and  that  iron  follows  the  loadstone,  and  chaff 
follows  amber :  as  for  amber,  why,  that,  mayhaps,  follows  the 
Antarctic  pole  :  emptiest  of  dreams  !  Others  have  come  down 
to  rocks  and  I  know  not  what  "  magnetic  mountains  " !  So 
has  ever  been  the  wont  of  mankind  :  homely  things  are  vile; 
things  from  abroad  and  things  afar  are  dear  to  them  and  the 
object  of  longing.  As  for  us,  we  are  habitants  of  this  very 
earth,  and  study  it  as  cause  of  this  mighty  effect.  Earth,  the 
mother  of  all,  hath  these  causes  shut  up  in  her  recesses :  all 
magnetic  movements  are  to  be  considered  with  respect  to  her 
law,  position,   constitution,  verticity,  poles,  equator,  horizon. 


l80  WILLIAM  GILBERT. 

meridians,  centre,  periphery,  diameter,  and  to  the  form  of  her 
whole  inward  substance.  So  hath  the  earth  been  ordered  by 
the  Supreme  Artificer  and  by  nature,  that  it  shall  have  parts 
unlike  in  position,  terminal  points  of  an  entire  and  absolute 
body,  and  such  points  dignified  by  distinct  functions,  whereby 
it  shall  itself  take  a  fixed  direction.  For  like  as  a  loadstone, 
when  in  a  suitable  vessel  it  is  floated  on  water,  or  when  it  is 
suspended  in  air  by  a  slender  thread,  does  by  its  native  ver- 
ticity,  according  to  the  magnetic  laws,  conform  its  poles  to  the 
poles  of  the  common  mother, — so,  were  the  earth  to  vary  from 
her  natural  direction  and  from  her  position  in  the  universe,  or 
were  her  poles  to  be  pulled  toward  the  rising  or  the  setting 
sun,  or  other  points  whatsoever  in  the  visible  firmament  (were 
that  possible),  they  would  recur  again  by  a  magnetic  move- 
ment to  north  and  south,  and  halt  at  the  same  points  where 
now  they  stand.  But  why  the  terrestrial  globe  should  seem 
constantly  to  turn  one  of  its  poles  toward  those  points  and 
toward  Cynosura  [constellation  of  the  Lesser  Bear],  or  why 
her  poles  should  vary  from  the  poles  of  the  ecliptic  by  23 
deg.  29  min.,  with  some  variation  not  yet  sufificiently  studied 
by  astronomers, — that  depends  on  the  magnetic  energy.  The 
causes  of  the  precession  of  the  equinoxes  and  of  the  progres- 
sion of  the  fixed  stars,  as  well  as  of  change  in  the  declinations 
of  the  sun  and  the  tropics,  are  traceable  to  magnetic  forces  : 
hence  we  have  no  further  need  of  Thebit  Bencora's  "  move- 
ment of  trepidation,"  which  is  at  wide  variance  with  observa- 
tions.'    A  rotating  needle  turns  to  conformity  with  the  situa- 

'  Ab{i  I'Hasan  Thdbet  Ben  Korrah,  celebrated  philosopher  and  geome- 
trician, born  in  Mesopotamia  A.D.  835-836,  was  appointed  by  Mo'tadhed 
Billah,  sixteenth  of  the  'Abbaside  Khalifs,  one  of  his  astrologers,  and  is  the 
author  of  numerous  treatises  on  mathematics  and  other  scientific  subjects,  as 
well  as  of  several  works  in  Syriac,  and  many  translations  in  Arabic,  the  bare 
mention  of  the  titles  of  which  take  up  nearly  two  folio  pages  of  Casiri's  Cata- 
logue. 


DIRECTION. 


z8i 


tion  of  the  earth,  and,  though  it  be  shaken  oft,  returns  still  to 
the  same  points.  For  in  far  northern  climes,  in  latitude  70  to 
80  deg.  (whither  in  the  milder  season  our  seamen  are  wont  to 
penetrate  without  injury  from  the  cold),  and  in  the  middle 
regions,  in  the  torrid  zone  under  the  equinoctial  line,  as  also 
in  all  maritime  regions  and  lands  of  the  southern  hemisphere, 
at  the  highest  latitudes  yet  known,  the  magnetic  needle  ever 
finds  its  direction  and  ever  tends  in  the  same  way  (barring  dif- 
ference of  variation)  on  this  side  of  the  equator  where  we 
dwell  and  in  the  other,  the  southern  part,  which,  though  less 
known,  has  been  to  some  extent  explored  by  our  sailors  :  and 
the  lily  of  the  mariner's  compass  ever  points  north.  Of  this, 
we  are  assured  by  the  most  illustrious  navigators  and  by  many 
intelligent  seamen.  The  same  was  pointed  out  to  me  and 
confirmed  by  our  most  illustrious  Neptune,  Francis  Drake, 
and  by  Thomas  Candish  [Cavendish],  that  other  world-ex- 
plorer. 

Our  terrella  teaches  the  same  lesson.  The  proposition  is 
demonstrated  on  a  spherical  loadstone.  Let  A,  B  be  the  poles ; 
CD,  an  iron  wire  placed  on  the  stone,  always  tends  direct  in 


the  meridian  to  the  poles  A,  B,  whether  the  centre  of  the  wire 
be  in  the  middle  line  or  equator  of  the  stone,  or  whether  it  be 
in  any  other  region  between  equator  and  poles,  as  H,  G,  F,  E.  * 


1 82  WILLIAM  GILBERT. 

So  the  point  of  a  magnetized  needle  looks  north  on  this  side 
of  the  equator :  on  the  other  side  the  crotch  is  directed  to  the 
south ;  but  the  point  or  lily  does  not  turn  to  the  south  below 
the  equator,  as  somebody  has  thought.  Some  inexperienced 
persons,  however,  who,  in  distant  regions  below  the  equator, 
have  at  times  seen  the  needle  grow  sluggish  and  less  prompt, 
have  deemed  the  distance  from  the  Arctic  pole  or  from  the 
magnetic  rocks  to  be  the  cause.  But  they  are  very  much 
mistaken,  for  it  has  the  same  power  and  adjusts  itself  as 
quickly  to  the  meridian  as  the  point  of  variation  in  southern 
regions  as  in  northern.  Yet  at  times  the  movement  appears 
to  be  slower,  the  point  on  which  the  compass  needle  is  poised 
becoming  in  time,  during  a  long  voyage,  rather  blunt,  or  the 
magnetized  needle  itself  having  lost  somewhat  of  its  acquired 
force  through  age  or  from  rusting.  This,  too,  may  be  tested 
experimentally  by  poising  the  versorium  of  a  sun-dial  on  a 
rather  short-pointed  needle  rising  perpendicularly  out  of  the 
surface  of  the  terrella.  The  magnetized  needle  turns  to  the 
poles  of  the  terrella,  and  quits  the  earth's  poles ;  for  a  general 
cause  that  is  remote  is  overcome  by  a  particular  cause  that 
is  present  and  strong.  Magnetized  bodies  incline  of  their 
own  accord  to  the  earth's  position,  and  they  conform  to  the 
terrella.  Two  loadstones  of  equal  weight  and  force  conform 
to  the  terrella  in  accordance  with  magnetic  laws.  Iron 
gets  force  from  the  loadstone  and  is  made  to  conform  to 
the  magnetic  movements.  Therefore  true  direction  is  the 
movement  of  a  magnetized  body  in  the  line  of  the  earth's  ver- 
ticity  toward  the  natural  position  and  unition  of  both,  their 
forms  being  in  accord  and  supplying  the  forces.  For  we  have, 
after  many  experiments  in  various  ways,  found  that  the  dis- 
posing and  ranging  of  the  magnetized  bodies  depends  on  the 
differences  of  position,  while  the  force  that  gives  the  motion  is 


DIRECTIVE  FORCE.  I83 

the  one  form  common  to  both ;  also  that  in  all  magnetic 
bodies  there  is  attraction  and  repulsion.  For  both  the  load- 
stone and  the  magnetized  iron  conform  themselves,  by  rota- 
tion and  by  dip,  to  the  common  position  of  nature  and  the 
earth.  And  the  earth's  energy,  with  the  force  inhering  in  it 
as  a  whole,  by  pulling  toward  its  poles  and  by  repelling,  ar- 
ranges in  order  all  magnetic  bodies  that  are  unattached  and 
lying  loose.  For  in  all  things  do  all  magnetic  bodies  conform 
to  the  globe  of  earth  in  accordance  with  the  same  laws  and  in 
the  same  ways  in  which  another  loadstone  or  any  magnetic 
body  whatsoever  conforms  to  the  terrella. 


CHAPTER  II. 

DIRECTIVE  (or  VERSORIAL)  FORCE,  WHICH  WE  CALL  VER- 
TICITY:  WHAT  IT  IS;  HOW  IT  RESIDES  IN  THE  LOAD- 
STONE ;  AND  HOW  IT  IS  ACQUIRED  WHEN  NOT  NAT- 
URALLY  PRODUCED. 

The  directive  force,  which  by  us  is  also  called  verticity,  is 
a  force  distributed  by  the  innate  energy  from  the  equator  in 
both  directions  to  the  poles.  That  energy,  proceeding  north 
and  south  to  the  poles,  produces  the  movement  of  direction, 
and  produces  also  constant  and  permanent  station  in  the  sys- 
tem of  nature,  and  that  not  in  the  earth  alone  but  in  all  mag- 
netic bodies  also.  Loadstone  occurs  either  in  a  special  vein 
or  in  iron  mines,  for,  being  a  homogenic  earth-substance  pos- 
sessing and  conceiving  a  primary  form,  it  becomes  converted 
into  or  concreted  with  a  stony  body  which,  in  addition  to  the 


I §4  WILLIAM  GILBERT, 

prime  virtues  of  the  form,  derives  from  different  beds  and 
mines,  as  from  different  matrices,  various  dissimilitudes  and 
differences,  and  very  many  secondary  qualities  and  varieties  of 
its  substance.  A  loadstone  mined  in  this  debris  of  the  earth's 
surface  and  of  its  projections,  whether  it  be  (as  sometimes 
found  in  China)  entire  in  itself,  or  whether  it  be  part  of  a  con- 
siderable vein,  gets  from  the  earth  its  form  and  imitates  the 
nature  of  the  whole.  All  the  inner  parts  of  the  earth  are  in 
union  and  act  in  harmony,  and  produce  direction  to  north  and 
south.  Yet  the  magnetic  bodies  that  in  the  topmost  parts  of 
the  earth  attract  one  another  are  not  true  united  parts  of  the 
whole,  but  are  appendages  and  agnate  parts  that  copy  the 
nature  of  the  whole ;  hence,  when  floating  free  on  water,  they 
take  the  direction  they  have  in  the  terrestrial  order  of  nature. 
=  We  once  had  chiselled  and  dug  out  of  its  vein  a  loadstone  20 
pounds  in  weight,  having  first  noted  and  marked  its  extremi- 
ties ;  then,  after  it  had  been  taken  out  of  the  earth,  we  placed 
it  on  a  float  in  water  so  it  could  freely  turn  about ;  straight- 
way that  extremity  of  it  which  in  the  mine  looked  north 
turned  to  the  north  in  water  and  after  a  while  there  abode ; 
for  the  extremity  that  in  the  mine  looks  north  is  austral  and  is 
attracted  by  the  north  parts  of  earth,  just  as  in  the  case  of 
iron,  which  takes  verticity  from  the  earth.  Of  these  points  we 
will  treat  later  under  the  head  of  "  Change  of  Verticity." 

But  different  is  the  verticity  of  the  inward  parts  of  the 
earth  that  are  perfectly  united  to  it  and  that  are  not  separated 
from  the  true  substance  of  the  earth  by  interposition  of  bodies, 
as  are  separated  loadstones  situated  in  the  outer  portion  of  the 
globe,  where  all  is  defective,  spoilt,  and  irregular.  Let  AB 
be  a  loadstone  mine,  and  between  it  and  the  uniform  earthen 
globe  suppose  there  are  various  earths  and  mixtures  that  in 
a  manner  separate  the  mine  from  the  true  globe  of  the  earth. 


DIRECTIVE  FORCE.  18$ 

It  is  therefore  informated  by  the  earth's  forces  just  as  CD, 
a  mass  of  iron,  is  in  air ;  hence  the  extremity  B  of  the  mine  or 
of  any  part  thereof  moves  toward  the  north  pole  G,  just  as 
does  C,  the  extremity  of  the  mass  of  iron,  but  not  A  nor  D, 
But  with  the  part  EF,  which  comes  into  existence  continuous 
with  the  whole  and  which  is  not  separated  from  it  by  any 


mixed  earthy  matter,  the  case  is  different.  For  if  the  part 
EF,  being  taken  out,  were  to  be  floated,  it  is  not  E  that  would 
turn  to  the  north  pole,  but  F.  Thus,  in  those  bodies  which 
acquire  verticity  in  the  air,  C  is  the  south  extremity  and  is  at- 
tracted by  the  north  pole  G.  In  those  which  come  into  exist- 
ence in  the  detrital  outermost  part  of  the  earth,  B  is  south, 
and  so  goes  to  the  north  pole.  But  these  parts  which,  deep* 
below,  are  of  even  birth  with  the  earth,  have  their  verticity 
regulated  differently.  For  here  F  turns  to  the  north  parts  of 
the  earth,  being  a  south  part ;  and  E  to  the  south  parts  of  the 
eairth,  being  a  north  part.  So  the  end  C  of  the  magnetic  body 
CD,  situate  near  the  earth,  turns  to  the  north  pole  ;  the  end  B  of 
the  agnate  body  BA  to  the  north  ;  the  end  E  of  the  inborn 
body  EF  to  the  south  pole — as  is  proved  by  the  following 
demonstration  and  as  is  required  by  all  magnetic  laws. 


1 86  WILLIAM  GILBERT. 

Describe  a  terrella  with  poles  A,  B  ;  from  its  mass  sepa- 
rate the  small  part  EF,  and  suspend  that  by  a  fine  thread  in  a 
cavity  or  pit  in  the  terrella.  E  then  does  not  seek  the  pole  A 
but  the  pole  B,  and  F  turns  to  A,  behaving  quite  differently 
from  the  iron  bar  CD;  for,  there,  C,  touching  a  north  part  of 
the  terrella,  becomes  magnetized  and  turns  to  A,  not  to  B. 
But  here  it  is  to  be  remarked  that  if  pole  A  of  the  terrella 
*  were  to  be  turned  toward  the  southern  part  of  the  earth,  still 


the  end  E  of  the  solitary  part  cut  out  of  the  terrella  and  not 
brought  near  the  rest  of  the  stone  would  turn  to  the  south  ; 
but  the  end  C  of  the  iron  bar  would,  if  placed  outside  the 
magnetic  field,  turn  to  the  north.  Suppose  that  in  the  un- 
broken terrella  the  part  EF  gave  the  same  direction  as  the 
whole ;  now  break  it  off  and  suspend  it  by  a  thread,  and  E  will 
turn  to  B  and  F  to  A.  Thus  parts  that  when  joined  with 
the  whole  have  the  same  verticity  with  it,  on  being  separated 
take  the  opposite  ;  for  opposite  parts  attract  opposite  parts, 
yet  this  is  not  a  true  opposition,  but  a  supreme  concordance 
and  a  true  and  genuine  conformance  of  magnetic  bodies  in 
nature,  if  they  be  but  divided  and  separated  ;  for  the  parts  thus 
divided  must  needs  be  carried  away  some  distance  above  the 
whole,  as  later  will  appear.  Magnetic  bodies  seek  formal  unity, 
and  do  not  so  much  regard  their  own  mass.     Hence  the  part 


DIRECTIVE  FORCE. 


187 


FE  is  not  attracted  into  its  pit,  but  the  moment  it  wanders  * 
abroad  and  is  away  from  it,  is  attracted  by  the  opposite  pole. 
But  if  the  part  FE  be  again  placed  in  its  pit  or  be  brought 


near  without  any  media  interposed,  it  acquires  the  original 
combination,  and,  being  again  a  united  portion  of  the  whole, 
co-operates  with  the  whole  and  readily  clings  in  its  pristine 
position,  while  E  remains  looking  toward  A  and  F  toward  By 
and  there  they  rest  unchanging. 

The  case  is  the  same  when  we  divide  a  loadstone  into  two* 
equal  parts  from  pole  to  pole.  In  the  figure,  a  spherical  stone 
is  divided  into  two  equal  parts  along  the  axis  AB  ;  hence, 
whether  the  surface  ^^  be  in  one  of  the  two  parts  supine  (as 
in  the  first  diagram),  or  prone  in  both  (as  in  the  second),  the  end* 
A  tends  to  B.  But  it  is  also  to  be  understood  that  the  point 
B  does  not  always  tend  sure  to  A,  for,  after  the  division,  the 
verticity  goes  to  other  points,  for  example  to  F,  G,  as  is  shown 


i88 


WILLIAM  GILBERT. 


in  Chapter  XIV  of  this  Third  Book.  LM,  too,  is  now  the 
axis  of  the  two  halves,  and  AB  is  no  longer  the  axis ;  for, 
once  a  magnetic  body  is  divided,  the  several  parts  are  integral 
and  magnetic,  and  have  vertices  proportional  to  their  mass, 
new  poles  arising  at  each  end  on  division.  But  the  axis  and 
poles  ever  follow  the  track  of  a  meridian,   because  the  force 


proceeds  along  the  stone's  meridian  circles  from  the  equinoc- 
tial to  the  poles  invariably,  in  virtue  of  an  innate  energy  that 
belongs  to  matter,  owing  to  the  long  and  secular  position,  and 
bearings  toward  the  earth's  poles,  of  a  body  possessing  the  fit 
properties  ;  and  such  body  is  endowed  with  force  from  the 
earth  for  ages  and  ages  continuously,  and  has  from  its  first  be- 
ginning stood  firmly  and  constantly  turned  toward  fixed  and 
determinate  points  of  the  same. 


HO  W  IRON  A  CQ  UIRES  VER  TICIT  Y  FROM  THE  LOADSTONE.    1 89 


CHAPTER   III. 

HOW    IRON    ACQUIRES    VERTICITY    FROM    THE     LOADSTONE, 
AND   HOW   THIS  VERTICITY   IS   LOST   OR   ALTERED. 

An  oblong  piece  of  iron,  on  being  stroked  with  a  loadstone, 
receives  forces  magnetic,  not  corporeal,  nor  inhering  in  or  con- 
sisting with  any  body,  as  has  been  shown  in  the  chapters  on 
coition.  Plainly,  a  body  briskly  rubbed  on  one  end  with  a 
loadstone,  and  left  for  a  long  time  in  contact  with  the  stone, 
receives  no  property  of  stone,  gains  nothing  in  weight  ;  for  if 
you  weigh  in  the  smallest  and  most  accurate  scales  of  a  gold- 
smith a  piece  of  iron  before  it  is  touched  by  the  loadstone  you 
will  find  that  after  the  rubbing  it  has  the  same  precise  weight, 
neither  less  nor  more.  And  if  you  wipe  the  magnetized  iron^ 
with  cloths,  or  if  you  rub  it  with  sand  or  with  a  whetstone,  it 
loses  naught  at  all  of  its  acquired  properties.  For  the  force  is 
diffused  through  the  entire  body  and  through  its  inmost  parts, 
and  can  in  no  wise  be  washed  or  wiped  away.  Test  it,  there- 
fore, in  fire,  that  fiercest  tyrant  of  nature.  Take  a  piece  of  iron 
the  length  of  your  hand  and  as  thick  as  a  goose-quill ;  pass  it 
through  a  suitable  round  piece  of  cork  and  lay  it  on  the  sur- 
face of  water,  and  note  the  end  of  the  bar  that  looks  north. 
Rub  that  end  with  the  true  smooth  end  of  a  loadstone ;  thus 
the  magnetized  iron  is  made  to  turn  to  the  north.  Take  off 
the  cork  and  put  that  magnetized  end  of  the  iron  in  the  fire  = 
till  it  just  begins  to  glow  ;  on  becoming  cool  again  it  will  re- 
tain the  virtues  of  the  loadstone  and  will  show  verticity,  though 
not  so  promptly  as  before,  either  because  the  action  of  the  fire 


190  WILLIAM  GILBERT. 

was  not  kept  up  long  enough  to  do  away  all  its  force,  or  be 
cause  the  whole  of  the  iron  was  not  made  hot,  for  the  property 
is  diffused  throughout  the  whole.  Take  off  the  cork  again, 
drop  the  whole  of  the  iron  into  the  fire,  and  quicken  the  fire 
with  bellows  so  that  it  becomes  all  alive,  and  let  the  glowing 
iron  remain  for  a  little  while.  After  it  has  grown  cool  again 
(but  in  cooling  it  must  not  remain  in  one  position)  put  iron  and 

*  cork  once  more  in  water,  and  you  shall  see  that  it  has  lost  its 
acquired  verticity.  All  this  shows  how  difficult  it  is  to  do 
away  with  the  polar  property  conferred  by  the  loadstone. 
And  were  a  small  loadstone  to  remain  for  as  long  in  the  same 
fire,  it  too  would  lose  its  force.  Iron,  because  it  is  not  so 
easily  destroyed  or  burnt  as  very  many  loadstones,  retains  its 
powers  better,  and  after  they  are  lost  may  get  them  back  again 
from  a  loadstone  ;  but  a  burnt  loadstone  cannot  be  restored. 

Now  this  iron,  stripped  of  its  magnetic  form,  moves  in  a  way 
different  from  any  other  iron,  for  it  has  lost  the  polar  prop- 
erty ;  and  though  before  contact  with  the  loadstone  it  may 
have  had  a  movement  to  the  north,  and  after  contact  toward 

•  the  south,  now  it  turns  to  no  fixed  and  determinate  point; 
but  afterward,  very  slowly,  after  a  long  time,  it  turns  un- 
steadily toward  the  poles,  having  received  some  measure  of 
force  from  the  earth.  There  is,  I  have  said,  a  twofold  cause 
of  direction, — one  native  in  the  loadstone  and  in  iron,  and  the 
other  in  the  earth,  derived  from  the  energy  that  disposes 
things.  For  this  reason  it  is  that  after  iron  has  lost  the 
faculty  of  distinguishing  the  poles  and  verticity,  a  tardy  and 
feeble  power  of  direction  is  acquired  anew  from  the  earth's 
verticity.  From  this  we  see  how  difficultly,  and  how  only  by 
the  action  of  intense  heat  and  by  protracted  firing  of  the  iron 
till  it  becomes  soft,  the  magnetic  force  impressed  in  it  is  done 
away.     When  this  firing  has  suppressed  the  acquired  polar 


HOW  IRON  ACQUIRES  VERTICITY  FROM  THE  LOADSTONE.   I9I 

power,  and  the  same  is  now  quite  conquered  and  as  yet  has 
not  been  called  to  life  again,  the  iron  is  left  a  wanderer,  and 
quite  incapable  of  direction. 

But  we  have  to  inquire  further  how  it  is  that  iron  remains 
possessed  of  verticity.  It  is  clear  that  the  presence  of  a  load- 
stone strongly  affects  and  alters  the  nature  of  the  iron,  also 
that  it  draws  the  iron  to  itself  with  wonderful  promptness. 
Nor  is  it  the  part  rubbed  only,  but  the  whole  of  the  iron,  that 
is  affected  by  the  friction  (applied  at  one  end  only),  and 
therefrom  the  iron  acquires  a  permanent  though  unequal 
power,  as  is  thus  proved. 

Rub  with  a  loadstone  a  piece  of  iron  wire  on  one  end  so  as* 
to  magnetize  it  and  to  make  it  turn  to  the  north  ;  then  cut  off 
part  of  it,  and  you  shall  see  it  move  to  the  north  as  before, 
though  weakly.  For  it  is  to  be  understood  that  the  loadstone 
awakens  in  the  whole  mass  of  the  iron  a  strong  verticity  (pro- 
vided the  iron  rod  be  not  too  long),  a  pretty  strong  verticity  in 
the  shorter  piece  throughout  its  entire  length,  and,  as  long  as 
the  iron  remains  in  contact  with  the  loadstone,  one  somewhat 
stronger  still.  But  when  the  iron  is  removed  from  contact  it 
becomes  much  weaker,  especially  in  the  end  not  touched  by 
the  loadstone.  And  as  a  long  rod,  one  end  of  which  is  thrust 
into  a  fire  and  made  red,  is  very  hot  at  that  end,  less  hot  in 
the  parts  adjoining  and  midway,  and  at  the  farther  end  may 
be  held  in  the  hand,  that  end  being  only  warm, — so  the  mag- 
netic force  grows  less  from  the  excited  end  to  the  other ;  but 
it  is  there  in  an  instant,  and  is  not  introduced  in  any  interval 
of  time  nor  successively,  as  when  heat  enters  iron,  for  the 
moment  the  iron  is  touched  by  the  loadstone  it  is  excited 
throughout.  For  example,  take  an  unmagnetized  iron  rod,  * 
4  or  5  inches  long :  the  instant  you  simply  touch  with  a  load- 


192  WILLIAM  GILBERT. 

Stone  either  end,  the  opposite  end  straightway,  in  the  twink- 
ling of  the  eye,  repels  or  attracts  a  needle,  however  quickly 
brought  to  it.' 


CHAPTER   IV. 

WHY  MAGNETIZED  IRON  TAKES  OPPOSITE  VERTICITY ;  AND 
WHY  IRON  TOUCHED  BY  THE  TRUE  NORTH  SIDE  OF 
THE  STONE  MOVES  TO  THE  EARTH'S  NORTH,  AND  WHEN 
TOUCHED  BY  THE  TRUE  SOUTH  SIDE  TO  THE  EARTH'S 
SOUTH:  IRON  RUBBED  WITH  THE  NORTH  POINT  OF  THE 
STONE  DOES  NOT  TURN  TO  THE  SOUTH,  NOR  Vice  versa, 
AS  ALL  WRITERS  ON  THE  LOADSTONE  HAVE  ERRONE- 
OUSLY  THOUGHT. 

It  has  already  been  shown  that  the  north  part  of  a  load- 
stone does  not  attract  the  north  part  of  another  stone,  but  the 
south  part,  and  that  it  repels  the  north  end  of  another  stone 
applied  to  its  north  end.  That  general  loadstone,  the  terres. 
trial  globe,  does  with  its  inborn  force  dispose  magnetized  iron, 
and  the  magnetic  iron  too  does  the  same  with  its  inborn  force, 
producing  movement  and  determining  the  direction.  For 
whether  we  compare  together  and  experiment  on  two  load- 
stones, or  a  loadstone  and  piece  of  iron,  or  iron  and  iron,  or 
dearth  and  loadstone,  or  earth  and  iron  conformated  by  the 
earth  or  deriving  force  from  the  energy  of  a  loadstone,  of 
necessity  the  forces  and  movements  of  each  and  all  agree  and 
harmonize  in  the  same  way. 

^  Dr.  J.    Lament's    "Handbuch  des   Magnetismus,"   Leipzig   1S67,    page 
383. 


WHY  MAGNETIZED  IRON  TAKES  OPPOSITE  VERTICITY.  1 93 

But  the  question  arises,  Why  does  iron  touched  with  load- 
stone take  a  direction  of  movement  toward  the  earth's  opposite 
pole  and  not  toward  that  pole  of  earth  toward  which  looked 
the  pole  of  the  loadstone  with  which  it  was  magnetized?  Iron 
and  loadstone,  we  have  said,  are  of  the  same  primary  nature : 
iron  when  joined  to  a  loadstone  becomes  as  it  were  one  body 
with  it,  and  not  only  is  one  extremity  of  the  iron  altered,  but 
the  rest  of  its  parts  are  affected.  Let  A  be  the  north  pole  of 
a  loadstone  to  which  is  attached  the  tip  of  an  iron  pointer: 
the  tip  is  now  the  south  part  of  the  iron,  because  it  is  con- 


tz>&=^ 


tiguous  to  the  north  part  of  the  stone;  the  crotch  of  the 
pointer  becomes  north.  For  were  this  contiguous  magnetic 
body  separated  from  the  pole  of  the  terrella  or  the  parts  nigh 
the  pole,  the  other  extremity  (or  the  end  which  when  there 
was  conjunction  was  in  contact  with  the  north  part  of  the 
stone)  is  south,  while  the  other  end  is  north.  So,  too,  if  a 
magnetized  needle  be  divided  into  any  number  of  parts 
however  minute,  those  separated  parts  will  take  the  same  direc- 
tion which  they  had  before  division.  Hence,  as  long  as  the 
point  of  the  needle  remains  at  A,  the  north  pole,  it  is  not  aus- 
tral, but  is,  as  it  were,  part  of  a  whole  ;  but  when  it  is  taken 
away  from  the  stone  it  is  south,  because  on  being  rubbed  it 
tended  toward  the  north  parts  of  the  stone,  and  the  crotch  (the 


^94 


WILLIAM  GILBERT. 


other  end  of  the  pointer)  is  north.  The  loadstone  and  the 
pointer  constitute  one  body :  B  is  the  south  pole  of  the  whole 
mass  ;  C  (the  crotch)  is  the  north  extremity  of  the  whole.  Even 
divide  the  needle  in  two  at  E,  and  E  will  be  south  as  regards 
the  crotch,  E  will  also  be  north  with  reference  to  B.  A  is  the 
true  north  pole  of  the  stone,  and  is  attracted  by  the  south  pole 
of  the  earth.  The  end  of  a  piece  of  iron  touched  with  the  true 
north  part  of  the  stone  is  south,  and  turns  to  the  north  pole  of 
the  stone  A  if  it  be  near ;  if  it  be  at  a  distance  from  the  stone, 
it  turns  to  the  earth's  north.  So  whenever  iron  is  magnetized 
it  tends  (if  free  and  unrestrained)  to  the  portion  of  the  earth 
*  opposite  the  part  toward  which  inclines  the  loadstone  at  which 
it  was  rubbed.  For  verticity  always  enters  the  iron  if  only  it 
be  magnetized  at  either  end.  Hence  all  the  needle  points  at 
B  acquire  the  same  verticity  after  being  separated,  but  it  is 


D  \^m/mmmi/^ ' 


the  opposite  verticity  to  that  of  the  pole  B  of  the  stone ;  and 
all  the  crotches  in  the  present  figure  have  a  verticity  opposite 
to  that  of  the  pole  E,  and  are  made  to  move  and  are  seized  by 
E  when  they  are  in  suitable  position.  The  case  is  as  in  the 
oblong  stone  FH,  cut  in  two  at  G,  where  F  and  H,  whether  the 
stone  be  whole  or  be  broken,  move  to  opposite  poles  of  the 


WHY  MAGNETIZED  IRON  TAKES  OPPOSITE   VERTICITY.   I95 

earth,  and  O  and  P  mutually  attract,  one  being  north,  the  other 
south.  For  if  in  the  whole  stone  H  was  south  and  F  norths 
then  in  the  divided  stone  P  will  be  north  with  respect  to  H  and 
O,  south  with  respect  to  F\  so,  too,  i^and  //"tend  toward  con- 
nection if  they  be  turned  round  a  little,  and  at  length  they 
come  together.  But  if  the  division  be  made  meridionally,  i.e., 
along  the  line  of  the  meridian  and  not  on  any  parallel  circle, 
then  the  two  parts  turn  about  and  A  pulls  B,  and  the  end  B 


is  attracted  to  A,  until,  being  turned  round,  they  form  connec- 
tion and  are  held  together.     For  this  reason,  iron  bars  placed  * 
on  parallels  near  the  equator  of  a  terrella  whose  poles  are  AB^ 
do  not  combine  and  do  not  cohere  firmly ;    but  when  placed 


alongside  on  a  meridian  line,  at  once  they  become  firmly  joined,  = 
not  only  on  the  stone  and  near  it,  but  at  any  distance  within 


196  WILLIAM  GILBERT. 

the  magnetic  field  of  the  controlling  loadstone.  Thus  they  are 
held  fast  together  at  E,  but  not  at  C  of  the  other  figure.  For 
the  opposite  ends  C  and  F  of  the  bars,  come  together  and 
cohere,  as  the  ends  A  and  B  of  the  stone  did.  But  the  ends 
are  opposite,  because  the  bars  proceed  from  opposite  poles  and 
parts  of  the  terrella  ;  and  C  is  south  as  regards  the  north  pole 
*A,  and  F  is  north  as  regards  the  south  pole  B.  Similarly,  too, 
they  cohere  if  the  rod  C(not  too  long)  be  moved  further  toward 
A,  and  the  rod  F  toward  B,  and  they  will  be  joined  on  the 
terrella  just  as  A  and  B  of  the  divided  stone  were  joined.     But 

♦  now  if  the  magnetized  needle  point  A  be  north,  and  if  with 
this  you  touch  and  rub  the  point  B  of  another  needle  that  ro- 
tates freely  but  is  not  magnetized,  B  will  be  north  and  will  turn 
to  the  south.  But  if  with  the  north  point  B  you  touch  still 
another  new  rotatory  needle  on  its  point,  that  point  again  will 
be  south,  and  will  turn  to  the  north :  a  piece  of  iron  not  only 
takes  from  the  loadstone,  if  it  be  a  good  loadstone,  the  forces 
needful  for  itself,  but  also,  after  receiving  them,  infuses  them 
into  another  piece,  and  that  into  a  third,  always  with  due  regard 
to  magnetic  law. 

In  all  these  our  demonstrations  it  is  ever  to  be  borne  in 
mind  that  the  poles  of  the  stone  as  of  the  iron,  whether  mag- 
netized or  not,  are  always  in  fact  and  in  their  nature  opposite  to 
the  pole  toward  which  they  tend,  and  that  they  are  thus  named 
by  us,  as  has  been  already  said.  For,  everywhere,  that  is  north 
which  tends  to  the  south  of  the  earth  or  of  a  terrella,  and  that 
is  south  which  turns  to  the  north  of  the  stone.    Points  that  are 

*  north  are  attracted  by  the  south  part  of  the  earth,  and  hence 
when  floated  they  tend  to  the  south.  A  piece  of  iron  rubbed 
with  the  north  end  of  a  loadstone  becomes  south  at  the  other 
end  and  tends  always  (if  it  be  within  the  field  of  a  loadstone 
and  near)  to  the  north  part  of  the  loadstone,  and  to  the  north 


MAGNETIZING  STONES  OF  DIFFERENT  SHAPES.       1 9/ 

part  of  the  earth  if  it  be  free  to  move  and  stand  alone  at  a  dis- 
tance from  the  loadstone.  The  north  pole  ^  of  a  loadstone 
turns  to  the  south  of  the  earth,  (9;  a  needle  magnetized  on 


.F 


its  point  by  the  part  A  follows  A,  because  the  point  has  been 
made  south.  But  the  needle  C,  placed  at  a  distance  from  the  = 
loadstone,  turns  its  point  to  the  earth's  north,  F,  for  that  point 
was  made  south  by  contact  with  the  north  part  of  the  loadstone. 
Thus  the  ends  magnetized  by  the  north  part  of  the  stone 
become  south,  or  are  magnetized  southerly,  and  tend  to  the 
earth's  north ;  the  ends  rubbed  with  the  south  pole  become 
north,  or  are  magnetized  northerly,  and  tend  to  the  earth's  south. 


CHAPTER  V. 

OF  MAGNETIZING  STONES  OF  DIFFERENT  SHAPES. 

Of  a  magnetized  piece  of  iron  one  extremity  is  north,  the 
other  south,  and  midway  is  the  limit  of  verticity :  such  limit,  in 
the  globe  of  the  terrella  or  in  a  globe  of  iron,  is  the  equinoctial 
circle.  But  if  an  iron  ring  be  rubbed  at  one  part  with  a  load- « 
stone,  then  one  of  the  poles  is  at  the  point  of  friction,  and  the 
other  pole  at  the  opposite  side  ;  the  magnetic  force  divides  the 
ring  into  two  parts  by  a  natural  line  of  demarkation,  which, 


198  WILLIAM  GILBERT. 

though  not  in  form,  is  in  its  power  and  effect  equinoctial.  But 
if  a  straight  rod  be  bent  into  the  form  of  a  ring  without  weld- 
ing and  unition  of  the  ends,  and  it  be  touched  in  the  middle 
with  a  loadstone,  the  ends  will  be  both  of  the  same  verticity. 

*  Take  a  ring,  whole  and  unbroken,  rubbed  with  a  loadstone  at 

*  one  point ;  then  cut  it  across  at  the  opposite  point  and  stretch 
it  out  straight :  again  both  ends  will  be  of  the  same  verticity, 
— ^just  like  an  iron  rod  magnetized  in  the  middle,  or  a  ring  not 
cohering  at  the  joint. 


CHAPTER  VI. 

WHAT  SEEMS  TO    BE  A  CONTRARY   MOVEMENT  OF  MAGNETIC 
BODIES  IS  THE  REGULAR  TENDENCE  TO  UNION. 

In  magnetic  bodies  nature  ever  tends  to  union — not  merely 
to  confluence  and  agglomeration,  but  to  agreement,  so  that  the 
force  that  causes  rotation  and  bearing  toward  the  poles  may 
not  be  disordered,  as  is  shown  in  various  ways  in  the  following 
example.     Let   CD  be  an   unbroken  magnetic  body,  with  C 


looking  toward  B,  the  earth's  north,  B  and  D  toward  A,  the 
*earth's  south.     Now  cut  it  in  two  in  the  middle,  in  the  equato|-, 


CONTRARY  MOVEMENT  OF  MAGNETIC  BODIES.        1 99 

and  then  E  will  tend  to  A  and  F  to  B,  For,  as  in  the  whole, 
so  in  the  divided  stone,  nature  seeks  to  have  these  bodies 
united ;  hence  the  end  E  properly  and  eagerly  comes  together 
again  with  F,  and  the  two  combine,  but  E  is  never  joined  to  D 
nor  F  to  C,  for,  in  that  case,  C  would  have  to  turn,  in  opposition, 
to  nature,  to  A,  the  south,  or  D  to  B,  the  north — which  were 
abnormal  and  incongruous.  Separate  the  halves  of  the  stone 
and  turnZ>  toward  C:  they  come  together  nicely  and  combine. 
For  D  tends  to  the  south,  as  before,  and  C  to  the  north  ;  E  and 
F,  which  in  the  mine  were  connate  parts,  are  now  greatly  at 
variance,  for  they  do  not  come  together  on  account  of  material 
afitinity,  but  take  movement  and  tendence  from  the  form. 
Hence  the  ends,  whether  they  be  conjoined  or  separate,  tend 
in  the  same  way,  in  accordance  with  magnetic  law,  toward  the 
earth's  poles  in  the  first  figure  of  the  stone,  whether  unbroken 
or  divided  as  in  the  second  figure  ;  and  FE  of  the  second  figure, 
when  the  two  parts  come  together  and  form  one  body,  is  as 
perfect  a  magnetic  mass  as  was  CD  when  first  produced  in  the 
mine;  and  FE,  placed  on  a  float,  turn  to  the  earth's  poles,* 
and  conform  thereto  in  the  same  way  as  the  unbroken  stone. 

This  agreement  of  the  magnetic  form  is  seen  in  the  shapes 
of  plants.     Let  AB  be  a  branch  of  ozier '  or  other  tree  that  * 


sprouts  readily ;  and  let  A  be  the  upper  part  of  the  branch 
and  be  the  part  rootward.     Divide  the  branch  at  CD.     Now, 

'  Ozier,  osier,  a  species  of  willow  {salix). 


200 


WILLIAM  GILBERT. 


the  extremity  CD^  if  skilfully  grafted  again  on  Z?,  begins  to 
grow,  just  as  B  and  A,  when  united,  become  consolidated  and 
germinate.  But  if  D  be  grafted  in  ^,  or  6^  on  B,  they  are  at 
variance  and  grow  not  at  all,  but  one  of  them  dies  because  of 
the  preposterous  and  unsuitable  apposition,  the  vegetative 
force,  which  tends  in  a  fixed  direction,  being  now  forced  into 
a  contrary  one. 


CHAPTER  VII.      • 

A  DETERMINATE  VERTICITY  AND  A  DIRECTIVE  POWER  MAKE 
MAGNETIC  BODIES  ACCORD,  AND  NOT  AN  ATTRACTIONAL 
OR  A  REPULSATIVE  FORCE,  NOR  STRONG  COITION  ALONE 
OR  UNITION. 

In  the  equinoctial  circle  A  there  is  no  coition  of  the  ends 
of  a  piece  of  iron  wire  with  the  terrella  ;  at  the  poles  the 


X^ 

^^^^'SA 

.   ^ 

/ 

1       ^ 

1 

1 

"  .Axis      dV 

I 

**■                  /■ 

m 

'^                  1 

\^ 

t                 / 

coition    is   very   strong.     The   greater  the  distance  from  the 
equinoctial  the  stronger  is  the  coition  with  the  terrella  itself, 


DISAGREEMENTS  OF  IRON  ON  THE  SAME  POLE.     201 

and  with  any  part  thereof,  not  with  the  pole  only.  But  the 
pieces  of  iron  are  not  made  to  stand  because  of  any  peculiar 
attracting  force  or  any  strong  combined  force,  but  because  of 
the  common  energy  that  gives  to  them  direction,  conformity, 
and  rotation.  For  in  the  region  B  not  even  the  minutest  bit* 
of  iron  that  weighs  almost  nothing  can  be  reared  to  the  per- 
pendicular by  the  strongest  of  loadstones,  but  adheres  ob- 
liquely. And  just  as  the  terrella  attracts  variously,  with  unlike* 
force,  magnetic  bodies,  so,  too,  an  iron  hump  (or  protuberance 
— nasits)  attached  to  the  stone  has  a  different  potency  according 
to  the  latitude  :  thus  the  hump  Z,  as  being  strongly  adherent, 
will  carry  a  greater  weight  than  M,  and  M  a  heavier  weight 
than  N.  But  neither  does  the  hump  rear  to  perpendicular  a 
bit  of  iron  except  at  the  poles,  as  is  shown  in  the  figure.  The 
hump  L  will  hold  and  lift  from  the  ground  two  ounces  of  solid 
iron,  yet  it  is  unable  to  make  a  piece  of  iron  wire  weighing* 
two  grains  stand  erect ;  but  that  would  not  be  the  case  if 
verticity  arose  from  strong  attraction,  or  more  properly  coi- 
tion, or  from  unition. 


CHAPTER  VIII. 

OF  DISAGREEMENTS  BETWEEN  PIECES  OF  IRON  ON  THE 
SAME  POLE  OF  A  LOADSTONE  ;  HOW  THEY  MAY  COME 
TOGETHER  AND   BE   CONJOINED. 

If  two  pieces  of  iron  wire  or  two  needles  above  the  poles 
of  a  terrella  adhere,  when  about  to  be  raised  to  the  perpen- 
dicular they  repel  each  other  at  their  upper  ends  and  present  * 
a  furcate  appearance  ;  and  if  one  end  be  forcibly  pushed  toward 


202  WILLIAM  GILBERT. 

the  other,  that  other  retreats  and  bends  back  to  avoid  the  asso- 
ciation, as  shown  in  the  figure.     A  and  B,  small  iron  rods. 


adhere  to  the  pole  obliquely  because  of  their  nearness  to  each 
other  :  either  one  alone  would  stand  erect  and  perpendicular. 
The  reason  of  the  obliquity  is  that  A  and  B,  having  the  same 
verticity,  retreat  from  each  other  and  fly  apart.  For  if  C  be  the 
north  pole  of  a  terrella,  then  the  ends  A  and  B  of  the  rods  are 
also  north,  while  the  ends  in  contact  with  and  held  fast  by  the 
pole  C  are  both  south.     But  let  the  rods  be  rather  long  (say 

1^  two  finger-breadths),  and  let  them  be  held  together  by  force : 
then  they  cohere  and  stand  together  like  friends,  nor  can  they 
be  separated  save  by  force,  for  they  are  held  fast  to  each  other 
magnetically,  and  are  no  longer  two  distinct  terminals  but  one 
only  and  one  body,  like  a  piece  of  wire  bent  double  and  made 
to  stand  erect. 

But  here  we  notice  another  curious  fact,  viz.,  that  if  the 
rods  be  rather  short,  not  quite  a  finger's  breadth  in  length,  or 

*  as  long  as  a  barley-corn,  they  will  not  unite  on  any  terms,  nor 
will  they  stand  up  together  at  all,  for  in  short  pieces  of  wire 
the  verticity  at  the  ends  farthest  from  the  terrella  is  stronger 
and  the  magnetic  strife  more  intense  than  in  longer  pieces. 


DISAGREEMENTS  OF  IRON  ON  THE  SAME  POLE.      203 

Therefore  they  do  not  permit  any  association,  any  fellowship. 
Again,  if  two  light  pieces  of  wire,  A  and  B,  be  suspended 


by  a  very  slender  thread  of  silk  filaments  not  twisted  but 
laid  together,' and  held  at  the  distance  of  one  barley-corn's* 
length  from  the  loadstone,  then  the  opposite  ends,  A  and  B, 
situate  within  the  sphere  of  influence  above  the  pole,  go  a 
little  apart  for  the  same  reason,  except  when  they  are  very 
near  the  pole  C  of  the  stone  :  in  that  position  the  stone  at- 
tracts them  to  the  one  point. 


•  See  Book  I,  Chapter  XII. 


204 


WILLIAM  GILBERT, 


CHAPTER  IX. 

DIRECTIONAL    FIGURES    SHOWING  THE    VARIETIES    OF  ROTA- 
TION. 

Having  now  sufficiently  shown,  according  to  magnetic  laws 
and  principles,  the  demonstrable  cause  of  the  motion  toward 
determinate  points,  we  have  next  to  show  the  movements. 
On  a  spherical  loadstone  having  the  poles  A,  B,  place  a  rotating 
needle  whose  point  has  been  magnetized  by  the  pole  A  :  that 
point  will  be  directed  steadily  toward  A  and  attracted  by  A, 


because,  having  been  magnetized  by  A,  it  accords  truly  and 
combines  with  A  ;  and  yet  it  is  said  to  be  opposite  because 
when  the  needle  is  separated  from  the  stone  it  moves  to  the 
opposite  part  of  earth  from  that  toward  which  the  loadstone's 
pole  A  moves.  For  if  A  be  the  north  pole  of  the  terrella,  the 
point  of  the  needle  is  its  south  end,  and  its  other  end,  the 
crotch,  points  to  B :  thus  B  is  the  loadstone's  south  pole, 
•  while  the  crotch  of  the  needle  is  the  needle's  north  end.  So, 
too,  the  point  is  attracted  by  EFGH  and  by  every  part  of  a 


FIGURES  SHOWING    2HE    VARIETIES  OF  ROTATION.     205 

meridian  from  the  equator  to  the  pole,  because  of  the  power 
of  directing ;  and  when  the  needle  is  in  those  places  on  the 
meridian  the  point  is  directed  toward  y^  ;  for  it  is  not  the 
point  A  but  the  whole  loadstone  that  makes  the  needle  turn, 
as  does  the  whole  earth  in  the  case  of  magnetic  bodies  turning 
to  the  earth. 

The  figure  following  shows  the  magnetic  directions  in  the 
right  sphere  of  a  loadstone  and  in  the  right  sphere  of  the 
earth,  also  the  polar  directions  to  the  perpendicular  of  the 
poles.  All  the  points  of  the  versorium  have  been  magnetized 
by  pole  A.  All  the  points  are  directed  toward  A  except  the 
one  that  is  repelled  by  B. 


t=t*=c> 


1^=0=:^ 


<?=o=:j 


The  next  figure  shows  horizontal  directions  above  the 
body  of  the  loadstone.  All  the  points  that  have  been  made 
south  by  rubbing  with  the  north  pole  or  some  point  around  the 
north  pole  A,  turn  to  the  pole  A  and  turn  away  from  the 
south  pole  B,  toward  which  all  the  crotches  are  directed. 

I  call  the  direction  horizontal  because  it  coincides  with 
the  plane  of  the  horizon ;  for  nautical  and  horological  instru- 
ments are  so  constructed  that  the  needle  shall  be  suspended 
or  supported  in  equilibrium  on  a  sharp  point,  which  prevents 
the  dip  of  the  needle,  as  we  shall  explain  later.     And  in  this 


206 


WILLIAM  GILBERT. 


way  it  best  serves  man's  use,  noting  and  distinguishing  all  the 
points  of  the  horizon  and  all  the  winds.  Otherwise  in  every 
oblique  sphere  (whether  terrella  or  earth)  the  needle  and  all 


magnetized  bodies  would  dip  below  the  horizon,  and,  at  the 
poles,  the  directions  would  be  perpendicular,  as  appears  from 
our  account  of  the  dip. 

The  next  figure  shows  a  spherical  loadstone  cut  in  two  at 
the  equator;  all  the  points  of  the   needles   have  been  mag- 


netized by  pole  A.     The  points  are  directed  in  the  centre  of 
the  earth  and  between  the  two  halves  of  the  terrel-la,  divided 


FIGURES  SHOWING   THE    VARIETIES  OF  ROTATION.     207 

in  the  plane  of  the  equator  as  shown  in  the  diagram.  The 
case  would  be  the  same  if  the  division  were  made  through  the 
plane  of  a  tropic  and  the  separation  and  distance  of  the  two 
parts  were  as  above,  with  the  division  and  separation  of  the 
loadstone  through  the  plane  of  the  equinoctial.  For  the 
points  are  repelled  by  C,  attracted  by  D,  and  the  needles  are 
parallel,  the  poles  or  the  verticity  at  both  ends  controlling 
them. 

The  next  figure  shows  half  of  a  terrella  by  itself,  and  its 
directions  differing  from  the  directions  given  by  the  two  parts 
in  the  preceding  figure,  which  were  placed  alongside.      All 


the  points  have  been  magnetized  by  A  ;  all  the  crotches  below, , 
except  the  middle  one,  tend  not  in  a  right  line  but  obliquely, 
to  the  loadstone,  for  the  pole  is  in  the  middle  of  the  plane 
that  before  was  the  plane  of  the  equinoctial.  All  points  mag- 
netized by  parts  of  the  loadstone  away  from  the  pole  move 
to  the  pole  (just  as  though  they  had  been  magnetized  by  the 
pole  itself)  and  not  to  the  place  of  friction,  wherever  that  may 
be  in  the  whole  stone  at  any  latitude  betwixt  pole  and  equa- 
tor. And  for  this  reason  there  are  only  two  differences  of 
regions — they  are  north  and  south  as  well  in  the  terrella  as  in 
the  great  globe  of  earth  ;  and  there  is  no  east,  no  west  place, 


208  WILLIAM  GILBERT. 

no  regions  truly  eastern  or  western,  but,  with  respect  to  each 
other,  east  and  west  are  simply  terms  signifying  toward  the 
east  or  west  part  of  the  heavens.  Hence  Ptolemy  seems  in 
the  Quadripartitum  to  err  in  laying  out  eastern  and  western 
divisions,  to  which  he  improperly  annexes  the  planets  ;  he  is 
followed  by  the  rabble  of  philosophasters  and  astrologers. 


CHAPTER   X.  . 

OF  THE  MUTATION  OF  VERTICITY  AND  MAGNETIC  PROPER- 
TIES, OR  OF  THE  ALTERATION  OF  THE  FORCE  AWA- 
KENED  BY  THE   LOADSTONE. 

Iron  excited  by  the  magnetic  influx  has  a  verticity  that  is 
pretty  strong,  yet  not  so  stable  but  that  the  opposite  parts 
may  be  altered  by  the  friction  not  only  of  a  stronger  but  of 
the  same  loadstone,  and  may  lose  all  their  first  verticity  and 
take  on  the  opposite.  Procure  a  piece  of  iron  wire  and  with 
the  self-same  pob  of  a  loadstone  rub  each  end  equally ;  pass 
the  wire  through  a  suitable  cork  float  and  put  it  in  the  water. 
Then  one  end  of  the  wire  will  look  toward  a  pole  of  the  earth 
whereto  that  end  of  the  loadstone  does  not  look.  But  which 
*  end  of  the  wire  ?  It  will  be  just  the  one  that  was  rubbed 
last.  Now  rub  with  the  same  pole  the  other  end  again,  and 
straightway  that  end  will  turn  in  the  opposite  direction. 
Again  rub  the  end  that  first  pointed  to  the  pole  of  the  load- 
stone, and  at  once  that,  having,  as  it  were,  obtained  its  orders 
{imperium  nactus),  will  go  in  the  direction  opposite  to  the  one 
it  took  last.     Thus  you  will  be  able  to  alter  again  and  again 


MUTATION  OF   VERTICITY.  209 

the  property  of  the  iron,  and  the  extremity  of  It  that  is  last 
rubbed  is  master.  And  now  merely  hold  for  a  while  the 
north  end  of  the  stone  near  the  north  end  of  the  wire  that 
was  last  rubbed,  not  bringing  the  two  into  contact,  but  at  the 
distance  of  one,  two,  or  even  three  finger-breadths,  if  the* 
stone  be  a  poAverful  one ;  again  the  iron  will  change  its  prop- 
erty and  will  turn  to  the  opposite  direction :  so  it  will,  too, 
though  rather  more  feebly,  if  the  loadstone  be  four  finger- 
breadths  away.  The  same  results  are  had  in  all  these  experi- 
ments whether  you  employ  the  south  or  the  north  part  of  the 
stone.  Verticity  can  also  be  acquired  or  altered  with  plates* 
of  gold,  silver,  and  glass  between  the  loadstone  and  the  end  of 
the  piece  of  iron  or  wire,  provided  the  stone  be  rather  power- 
ful, though  the  plates  of  metal  be  touched  neither  by  the 
stone  nor  by  the  iron.  And  these  changes  of  verticity  occur 
in  cast-iron.  But  what  is  imparted  or  excited  by  one  pole  of 
the  loadstone  is  expelled  and  annulled  by  the  other,  which 
confers  new  force.  Nor  is  a  stronger  loadstone  needed  to 
make  the  iron  put  off  the  weaker  and  sluggish  force  and  to 
put  on  a  new.  Neither  is  the  iron  "  made  drunken"  {inebri- 
atur)  by  equal  forces  of  loadstone,  so  that  it  becomes  "  unde- 
cided and  neutral,"  as  Baptista  Porta  maintains.  But  by  one 
same  loadstone,  and  by  loadstones  endowed  with  equal  power 
and  strength,  the  force  is  altered,  changed,  incited,  renewed, 
driven  out.  The  loadstone  itself,  however,  is  not  robbed,  by 
friction  with  another  bigger  or  stronger  stone,  of  its  property 
and  verticity,  nor  is  it  turned,  when  on  a  float,  to  the  oppo- 
site direction  or  to  another  pole  different  from  that  toward 
which,  by  its  own  nature  and  verticity,  it  tends.  For  forces 
that  are  innate  and  long  implanted  inhere  more  closely,  nor* 
do  they  easily  retire  from  their  ancient  seats ;  and  what  is  the 
growth  of  a  long  period  of  time  is  not  in  an  instant  reduced 


.210  WILLIAM  GILBERT. 

to  nothing  unless  that  in  which  it  inheres  perishes.  Neverthe- 
less change  comes  about  in  a  considerable  interval  of  time, 
e.g.,  a  year  or  two,  sometimes  in  a  few  months — to  wit,  when 
a  weaker  loadstone  remains  applied,  in  a  way  contrary  to 
the  order  of  nature,  to  a  stronger,  i.e.,  with  the  north  pole  of 
one  touching  the  north  pole  of  the  other,  or  the  south  of  one 
touching  the  other's  south.  Under  such  conditions,  in  the 
lapse  of  time  the  weaker  force  declines. 


CHAPTER  XL 

OF  FRICTION  OF  IRON  WITH  THE  MID  PARTS  OF  A  LOAD- 
STONE BETWEEN  THE  POLES,  AND  AT  THE  EQUINOCTIAL 
CIRCLE  OF  A  TERRELLA. 

Take  a  piece  of  iron  wire  not  magnetized,  three  finger- 
widths  long  ('twill  be  better  if  its  acquired  verticity  be  rather 
weak  or  deformated  by  some  process) ;  touch  and  rub  it  with 
the  equator  of  the  terrella  exactly  on  the  equinoctial  line 
along  its  whole  tract  and  length,  only  one  end,  or  both  ends, 
or  the  whole  of  the  iron,  being  brought  into  contact.  The 
wire  thus  rubbed,  run  through  a  cork  and  float  it  in  water. 
*  It  will  go  wandering  about  without  any  acquired  verticity,  and 
the  verticity  it  had  before  will  be  disordered.  But  if  by  chance 
it  should  be  borne  in  its  wavering  toward  the  poles,  it  will  be 
feebly  held  still  by  the  earth's  poles,  and  finally  will  be  en- 
dowed with  verticity  by  the  energy  of  the  earth. 


EXISTENCE  OF   VERTICITY  IN  SMELTED  IRON.       211 


CHAPTER  XII. 

HOW  VERTICITY  EXISTS  IN  ALL  SMELTED  IRON  NOT  EXCITED 
BY  THE   LOADSTONE. 

Hitherto  we  have  declared  the  natural  and  innate  causes 
and  the  powers  acquired  through  the  loadstone ;  but  now  we 
are  to  investigate  the  causes  of  the  magnetic  virtue  existing 
in  manufactured  iron  not  magnetized  by  the  loadstone.  The 
loadstone  and  iron  present  and  exhibit  to  us  wonderful  subtile 
properties.  It  has  already  oft  been  shown  that  iron  not  ex- 
cited by  the  loadstone  turns  to  north  and  south  ;  further,  that 
it  possesses  verticity,  i.e.,  distinct  poles  proper  and  peculiar  to 
itself,  even  as  the  loadstone  or  iron  rubbed  with  the  loadstone. 
This  seemed  to  us  at  first  strange  and  incredible :  the  metal, 
iron,  is  smelted  out  of  the  ore  in  the  furnace,  flows  out  of  the 
furnace,  and  hardens  in  a  great  mass ;  the  mass  is  cut  up  in 
great  workshops  and  drawn  out  into  iron  bars,  and  from  these 
again  the  smith  fashions  all  sorts  of  necessary  implements  and 
objects  of  iron.  Thus  the  same  mass  is  variously  worked  and 
transformed  into  many  shapes.  What,  then,  is  it  that  pre- 
serves the  verticity,  or  whence  is  it  derived?  First  take  a 
mass  of  iron  as  produced  in  the  first  iron-works.  Get  a  smith 
to  shape  a  mass  weighing  two  or  three  ounces,  on  the  anvil, 
into  an  iron  bar  one  palm  or  nine  inches  long.  Let  the  smith 
stand  facing  the  north,  with  back  to  the  south,  so  that  as  he* 
hammers  the  red-hot  iron  it  may  have  a  motion  of  extension 
northward ;  and  so  let  him  complete  the  task  at  one  or  two 
heatings  of  the  iron  (if  needed) ;  but  ever  while  he  hammers 


212 


WILLIAM  GILBERT. 


and  lengthens  it,  have  him  keep  the  same  point  of  the  iron 
looking  north,  and  lay  the  finished  bar  aside  in  the  same  direc- 
tion. In  this  way  fashion  two,  three,  or  more,  yea  one  hun- 
dred or  four  hundred  bars:  it  is  plain  that  all  the  bars  so 
hammered  out  toward  the  north  and  so  laid  down  while  cool- 
ing will  rotate  round  their  centres  and  when   afloat  (being 


passed  through  suitable  pieces  of  cork)  will  move  about  in 
water,  and,  when  the  end  is  duly  reached,  will  point  north. 
And  as  an  iron  bar  takes  verticity  from  the  direction  in  which 
it  lies  while  being  stretched,  or  hammered,  or  pulled,  so  too 

♦  will  iron  wire  when  drawn  out  toward  any  point  of  the  horizon 
between  east  and  south  or  between  south  and  west,  or  con- 

♦  versely.    Nevertheless,  when  the  iron  is  directed  and  stretched 


EXISTENCE   OF    VERTICITY  IN  SMELTED  IRON.       213 

rather  to  a  point  east  or  west,  it  takes  almost  no  verticity,  or 
a  very  faint  verticity.  This  verticity  is  acquired  chiefly 
through  the  lengthening.  But  when  inferior  iron  ore,  in 
which  no  magnetic  properties  are  apparent,  is  put  in  the  fire* 
(its  position  with  reference  to  the  world's  poles  being  noted) 
and  there  heated  for  eight  or  ten  hours,  then  cooled  away 
from  the  fire  and  in  the  same  position  with  regard  to  the 
poles,  it  acquires  verticity  according  to  its  position  during 
heating  and  cooling. 

Let  a  bar  of  iron  be  brought  to  a  white  heat  in  a  strong* 
fire,  in  which  it  lies  meridionally,  i.e.,  along  the  track  of  a 
meridian  circle ;  then  take  it  out  of  the  fire  and  let  it  cool  and 
return  to  the  original  temperature,  lying  the  while  in  the  same 
position  as  before :  it  will  come  about  that,  through  the  like 
extremities  having  been  directed  toward  the  same  poles  of  the 
earth,  it  will  acquire  verticity;  and  that  the  extremity  that 
looked  north  when  the  bar,  before  the  firing,  was  floated  in 
water  by  means  of  a  cork,  if  now  the  same  end  during  the 
firing  and  the  cooling  looked  southward,  will  point  to  the 
south.  If  perchance  the  turning  to  the  pole  should  at  any 
time  be  weak  and  uncertain,  put  the  bar  in  the  fire  again,  take 
it  out  when  it  has  reached  white  heat,  cool  it  perfectly  as  it 
lies  pointing  in  the  direction  of  the  pole  from  which  you  wish 
it  to  take  verticity,  and  the  verticity  will  be  acquired.  Let  it 
be  heated  again,  lying  in  the  contrary  direction,  and  while  yet* 
white-hot  lay  it  down  till  it  cools  ;  for,  from  the  position  in 
cooling  (the  earth's  verticity  acting  on  it),  verticity  is  infused 
into  the  iron  and  it  turns  toward  points  opposite  to  the 
former  verticity.  So  the  extremity  that  before  looked  north 
now  turns  to  the  south.  For  these  reasons  and  in  these  ways 
does  the  north  pole  of  the  earth  give  to  that  extremity  of  the* 
iron  which  is  turned  toward  it  south  verticity ;  hence,  too,  that 


214  WILLIAM  GILBERT 

extremity  is  attracted  by  the  north  pole.  And  here  it  is  to  be 
observed  that  this  happens  with  iron  not  only  when  it  cools 
lying  in  the  plane  of  the  horizon,  but  also  at  any  inclination 
thereto,  even  almost  up  to  perpendicular  to  the  centre  of  the 
earth.  Thus  heated  iron  more  quickly  gets  energy  (strength) 
and  verticity  from  the  earth  in  the  very  process  of  returning 
to  soundness  in  its  renascence,  so  to  speak  (wherein  it  is  trans- 

*  formated),  than  when  it  simply  rests  in  position.  This  experi- 
ment is  best  made  in  winter  and  in  a  cold  atmosphere,  when 
the  metal  returns  more  surely  to  the  natural  temperature 
than  in  summer  and  in  warm  climates.^ 

Let  us  see  also  what  position  alone,  without  fire  and  heat, 
and  what  mere  giving  to  the  iron  a  direction  toward  the  earth's 
poles  may  do.     Iron  bars  that  for  a  long  time — twenty  years 

*or  more — have  lain  fixed  in  the  north  and  south  position,  as 
bars  are  often  fixed  in  buildings  and  in  glass  windows — such 
bars,  in  the  lapse  of  time,  acquire  verticity,  and  whether  sus- 
pended in  air  or  floated  by  corks  on  water  turn  to  the  pole 
toward  which  they  used  to  be  directed,  and  magnetically 
attract  and  repel  iron  in  equilibrium ;  for  great  is  the  effect  of 
long-continued  direction  of  a  body  toward  the  poles.  This, 
though  made  clear  by  plain  experiment,  gets  confirmation  for 
what  we  find  in  a  letter  written  in  Italian  and  appended  to  a 
work  by  Master  Philip  Costa,  of  Mantua,  also  in  Italian,  Of 
the  Cojnpounding  of  Antidotes,  which,  translated,  is  as  follows: 
"At  Mantua,  an  apothecary  showed  to  me  a  piece  of  iron 
completely  turned  to  loadstone,  so  attracting  other  iron  that  it 
might  be  compared  to  a  loadstone.  But  this  piece  of  iron, 
after  it  had  for  a  long  time  supported  a  terra-cotta  ornament 
on  the  tower  of  the  Church  of  San  Agostino  at  Rimini,  was  at 


'See  John  Farrar's  "Elem.  of  Elect,  and  Magn,,"  1826,  pages  261',  202. 


EXISTENCE   OF   VERTICITY  IN  SMELTED  IRON.       21$ 

last  bent  by  the  force  of  the  winds  and  so  remained  for  ten 
years.  The  friars,  wishing  to  have  it  restored  to  its  original 
shape,  gave  it  to  a  blacksmith,  and  in  the  smithy  Master 
Giulio  Cesare,  prominent  surgeon,  discovered  that  it  resembled 
loadstone  and  attracted  iron.  The  effect  was  produced  by 
long-continued  lying  in  the  direction  of  the  poles.^  It  is  well, 
therefore,  to  recall  what  has  already  been  laid  down  with 
regard  to  alteration  of  verticity,  viz.,  how  that  the  poles  of 
iron  bars  are  changed  when  a  loadstone  simply  presents  its 
pole  to  them  and  faces  them  even  from  some  distance.  Surely 
in  a  like  way  does  that  great  loadstone  the  earth  affect  iron 
and  change  verticity.  For  albeit  the  iron  does  not  touch  the 
earth's  pole  nor  any  magnetic  portion  of  the  earth,  still  the 
verticity  is  acquired  and  altered — not  that  the  earth's  pole,  that 
identical  point  lying  thirty-nine  degrees  of  latitude,  so  great  a 
number  of  miles,  away  from  this  City  of  London,  changes  the 
verticity,  but  that  the  entire  deeper  magnetic  mass  of  the 
earth  which  rises  between  us  and  the  pole,  and  over  which 


*  It  is  said  by  Humboldt  {Cosmos,  1849,  Vol.  II,  page  718,  note)  that  this 
observation,  the  first  of  the  kind,  was  made  on  the  tower  of  the  Church  of  the 
Augustines  at  Mantua  (Mantova),  and  that  Grimaldi  and  Gassendi  were  ac- 
quainted with  similar  instances  (the  cross  of  the  Church  of  Saint  Jean,  at  Aix, 
in  Provence),  all  occurring  in  geographical  latitudes  where  the  inclination  of  the 
magnetic  needle  is  very  considerable.  Some  writers  give  Gassendi's  observa- 
tion as  occurring  during  1632.  (See  Rohaulti,  Physica,  1718,  Par.  Ill,  Cap.  8, 
p.  399;  or  Rohault's  "  System  of  Nat.  Phil.,"  1728,  page  176.) 

"  As  the  iron  cross  of  an  hundred  weight  upon  the  Church  of  Saint  John  in 
Ariminum,  or  that  Load-ston'd  iron  of  Caesar  Moderatus,  set  down  by  Aldro- 
vandus."     (Sir  Thomas  Brown,  Pseudoloxia  Epidemica,  1658,  page  66.) 

Consult  "  Lettera  dell'  Eccel.  Cavallara  "  Mantova  1586,  for  a  de- 
tailed account  of  this  discovery,  made  January  6  of  the  last-named  year.  The 
iron  rod  supported  a  brick  ornament  in  the  form  of  an  acorn,  and  stood  on  a 
pyramid  at  the  summit  of  the  belfry  of  the  Church  of  St.  John  the  Baptist  at 
Rimini,  belonging  to  the  monks  of  St.  Augustine.  See  Cabeo,  Philos.  Magn., 
page  62  ;  "  Ulysses  Aldrovandi,  Patr.  Bonon. . .  .Barthol.  Ambros  ....,"  Lib. 
I,  Cap.  VI,  p.  134. 


2l6  WILLIAM  GILBERT. 

stands  the  iron — that  this,  with  the  energy  residing  within  the 
field  of  the  magnetic  force,  the  matter  of  the  entire  orb  con- 
spiring, produces  verticity  in  bodies.  For  everywhere  within 
the  sphere  of  the  magnetic  force  does  the  earth's  magnetic 
effluence  reign,  everywhere  does  it  alter  bodies.  But  those 
bodies  that  are  most  like  to  it  and  most  closely  alHed,  it  rules 
and  controls,  as  loadstone  and  iron.  For  this  reason  it  is  not 
altogether  superstitious  and  silly  in  many  of  our  affairs  and 
businesses  to  note  the  positions  and  configurations  of  coun- 
tries, the  points  of  the  horizon  and  the  locations  of  the  stars. 
For  as  when  the  babe  is  given  forth  to  the  light  from  the 
mother's  womb  and  gains  the  power  of  respiration  and  certain 
animal  functions,  and  as  the  planets  and  other  heavenly  bodies, 
according  to  their  positions  in  the  universe  and  according  to 
their  configuration  with  the  horizon  and  the  earth,  do  then 
impart  to  the  new-comer  special  and  peculiar  qualities;  so  a 
piece  of  iron,  while  it  is  being  wrought  and  lengthened,  is 
affected  by  the  general  cause,  the  earth,  to  wit ;  and  while  it  is 
coming  back  from  the  fiery  state  to  its  original  temperature  it 
becomes  imbued  with  a  special  verticity  according  to  its  posi- 
*tion.  Long  bars  have  sometimes  the  same  verticity  at  both 
ends,  and  hence  they  have  a  wavering  and  ill-regulated  motion 
on  account  of  their  length  and  of  the  aforesaid  manipulations, 
just  as  when  an  iron  wire  four  feet  long  is  rubbed  at  both  ends 
with  one  same  pole  of  a  loadstone. 


ONLY  MAGNETIC  BODIES  IMBUED    WITH   VERTICITY,     21/ 


CHAPTER   XIII. 

WHY  NO  OTHER  BODIES  SAVE  THE  MAGNETIC  ARE  IMBUED 
WITH  VERTICITY  BY  FRICTION  WITH  A  LOADSTONE; 
AND  WHY  NO  BODY  NOT  MAGNETIC  CAN  IMPART  AND 
AWAKEN   THAT  FORCE. 

Wood  floating  on  water  never  turns  by  its  own  forces 
toward  the  poles  of  the  world  save  by  chance :  so  neither 
threads  of  gold,  silver,  copper,  zinc,  lead,  nor  glass,  when 
passed  through  cork  and  floated,  have  ever  sure  direction  ; 
and,  therefore,  when  rubbed  with  a  loadstone  they  show 
neither  poles  nor  points  of  variation ;  for  bodies  that  do  not 
of  their  own  accord  turn  toward  the  poles  and  are  not  obedi- 
ent to  the  earth  are  in  no  wise  governed  by  the  loadstone's 
touch ;  neither  has  the  energy  of  the  loadstone  entrance  into 
their  interior,  nor  are  their  forms  excited  magnetically ;  nor,  if 
the  energy  did  enter  in,  could  it  effect  aught,  for  the  reason 
that  there  are  no  primary  qualities  in  such  bodies,  mixed  as 
they  are  with  a  variety  of  efflorescent  humors  and  degenerate 
from  the  primal  property  of  the  globe.  On  the  other  hand  the 
properties  of  iron  which  are  primal  are  awakened  by  approach 
of  a  loadstone :  like  brute  animals  and  men  when  awakened 
out  of  sleep,  the  properties  of  iron  now  move  and  put  forth 
their  strength. 

Here  we  must  express  wonder  at  a  manifest  error  of  Bap- 
tista  Porta,  who,  though  he  properly  refuses  assent  to  the 
inveterate  falsehood  about  a  force  the  opposite  of  the  mag- 
netic, imparts  a  still  falser  opinion,  to  wit,  that  iron  rubbed 


21 8  WILLIAM  GILBERT. 

with  diamond  turns  to  the  north.  "  If,"  he  writes,  "we  rub  an 
iron  needle  on  diamond,  and  then  put  it  in  a  boat  or  on  a 
straw  or  suspend  it  properly  with  a  thread,  at  once  it  turns  to 
the  north  like  iron  rubbed  on  a  loadstone,  or  perhaps  a  little 
more  sluggishly.  Nay — and  this  is  worthy  of  remark — the 
opposite  part,  like  the  loadstone  itself  at  its  south  end,  repels 
iron,  and  when  we  experimented  with  a  multitude  of  small 
iron  rods  in  water,  they  all  stood  at  equal  distances  apart  and 
pointed  north."  Now  this  is  contrary  to  our  magnetic  rules ; 
and  hence  we  made  the  experiment  ourselves  with  seventy-five 
'  diamonds  in  presence  of  many  witnesses,  employing  a  number 
of  iron  bars  and  pieces  of  wire,  manipulating  them  with  the 
greatest  care  while  they  floated  in  water,  supported  by  corks ; 
yet  never  was  it  granted  me  to  see  the  effect  mentioned  by 
Porta.  He  was  led  astray  by  the  verticity  of  the  iron  in  the 
bars  or  wires  got  from  the  earth  (as  shown  above) ;  the  iron  of 
itself  tended  toward  its  determinate  pole,  and  Porta,  ignorant 
of  this,  supposed  the  thing  was  done  by  the  diamond.  But  let 
searchers  of  the  things  of  nature  beware  lest  they  be  further 
deluded  by  their  own  faultily  observed  experiments,  and  lest, 
with  errors  and  blunders,  they  throw  into  confusion  the  repub- 
lic of  letters.  Diamond  {adamas)  is  sometimes  called  siderite 
{siderites),  not  because  it  is  ferruginous  or  that  it  attracts  iron 
{aidrfpos,  sideros),  but  on  account  of  its  glister,  like  that  of 
shining  iron  ;  this  brilliance  is  possessed  by  the  finest  diamonds. 
On  account  of  this  confusion  of  names  many  effects  are  cred- 
ited to  diamond  that  in  fact  belong  to  the  loadstone  siderite.^ 

1  See  Book  I,  Chap.  II. 


POSITION  DOES  NOT  AFFECT    VERTICITY.  2ig 


CHAPTER  XIV. 

THE  POSITION  OF  A  LOADSTONE,  NOW  ABOVE,  ANON  BENEATH, 
A  MAGNETIC  BODY  SUSPENDED  IN  EQUILIBRIUM,  ALTERS 
NEITHER  THE  FORCE  NOR  THE  VERTICITY  OF  THE  MAG- 
NETIC  BODY. 

This  point  we  may  not  rightly  pass  by,  because  we  must 
correct  an  error  that  has  lately  arisen  out  of  a  faulty  observa- 
tion of  Baptista  Porta ;  out  of  this  erroneous  judgment.  Porta, 
by  vain  repetition,  makes  three  chapters,  viz.,  the  eighth,  the 
thirty-first,  and  the  sixty-second.  Now,  if  a  loadstone  or  a 
piece  of  iron  suspended  in  equilibrium  or  floating  in  water  is 
attracted  or  controlled  by  another  piece  of  iron  or  another 
loadstone  held  above  it,  the  stone  or  the  iron  does  not  turn  to 
the  opposite  direction  when  you  apply  the  second  iron  or  stone 
beneath  ;  on  the  contrary,  the  ends  of  the  floating  loadstone  or 
of  the  floating  iron  will  ever  turn  to  the  same  points  of  the 
stone,  however  the  loadstone  or  the  iron  may  be  suspended  in 
equilibrium  or  whether  they  be  mounted  on  a  point  so  that 
they  may  revolve  freely.  Porta  was  led  into  error  by  the  un- 
even shape  of  some  loadstone  or  by  the  fact  that  he  did  not 
manage  the  experiment  aright.  Thus  he  is  badly  mistaken, 
thinking  it  fair  to  infer  that,  as  the  loadstone  has  a  north  and 
a  south  pole,  it  has  also  an  east  and  a  west,  a  superior  and  an 
inferior,  pole.  So  do  many  vain  imaginations  arise  out  of  mis- 
takes committed  and  accepted  as  true  judgments. 


220 


WILLIAM   GILBERT. 


CHAPTER   XV. 

THE  POLES,  EQUATOR,  CENTRE,  ARE  PERMANENT  AND  STABLE 
IN  THE  UNBROKEN  LOADSTONE;  WHEN  IT  IS  REDUCED 
IN  SIZE  AND  A  PART  TAKEN  AWAY,  THEY  VARY  AND 
OCCUPY   OTHER  POSITIONS.  , 

Let  AB  be  a  terrella,  E  its  centre,  DF  its  diameter  (and 
also  its  equinoctial  circle).  If  you  cut  out  a  piece  (for  instance 
along  the  Arctic  circle)  GH,  it  is  evident  that  the  pole  which 
before  was  at  A  now  has  its  seat  at  /.     But  the  centre  and  the 


%  equinoctial  circle  recede  only  toward  B,  so  as  always  to  be  in 
the  middle  of  the  mass  that  remains  between  the  plane  of  the 
Arctic  circle  6^//7and  the  Antarctic  pole  B.  Thus  the  segment 
of  the  terrella  between  the  plane  of  the  former  equinoctial  cir- 
cle DEF  (that  is  of  the  equinoctial  circle  which  existed  before 


THE  POLES  IN  BROKEN  AND    UNBROKEN  LOADSTONE.   221 

the  part  was  cut  away)  and  the  newly  acquired  equator  MLN 
will  always  be  equal  to  one  half  of  the  part  cut  off,  GIHA. 
But  if  the  part  be  cut  from  the  side  CD  then  the  poles  and  the* 
axis  will  not  be  in  the  line  AB  but  in  EF\  and  the  axis  is 


■^A. 


E  S 


changed  in  the  same  proportion  as  the  equator  in  the  previous 
figure.  For  these  points  of  forces  and  of  energy,  or  rather 
these  terminals  of  forces  that  flow  from  the  entire  form,  are 
moved  forward  by  change  of  mass  or  of  figure ;  as  all  these 
points  result  from  the  joint  action  of  the  whole  and  of  all  the 
parts  united,  and  verticity  or  polarity  is  not  a  property  innate  in 
the  part  or  in  any  fixed  point,  but  a  tendency  of  the  force  to 
such  part.  And  as  aterrella  dug  out  of  the  earth  has  no  longer 
the  poles  and  the  equator  of  the  earth  but  special  poles  and 
equator  of  its  own,  so,  too,  if  the  terrella  be  cut  in  two  again, 
these  points  and  distinctions  of  its  forms  and  powers  migrate 
to  other  parts.  But  if  the  loadstone  be  in  any  way  divided 
either  on  the  parallels  or  on  the  meridians  so  that  in  conse- 
quence of  the  change  of  its  shape  either  the  poles  or  the  equator 
migrate  to  other  seats,  then  if  the  part  that  has  been  cut  off 


222  WILLIAM  GILBERT. 

be  but  set  in  its  natural  position  and  conjoined  to  the  rest, 
though  they  be  not  cemented  or  otherwise  fastened  together, 
the  terminal  points  go  back  again  to  the  former  places  as 
though  no  part  of  the  body  had  been  cut  away.  When  the 
body  is  whole  the  form  remains  whole  ;  but  when  the  mass  of 
the  body  is  reduced,  a  new  whole  results,  and  a  new  wholeness 
necessarily  arises  in  each  minutest  piece  of  loadstone,  even  in 
magnetic  gravel  and  fine  sand. 


CHAPTER   XVI. 

IF  THE  SOUTH  PART  OF  A  LOADSTONE  HAVE  A  PART  BROKEN 
OFF,  SOMEWHAT  OF  POWER  IS  TAKEN  AWAY  FROM  THE 
NORTH  PART  ALSO. 

For  though  the  south  part  of  magnetic  iron  is  attracted  by 
the  north  part  of  the  loadstone,  still  the  south  part  of  the  stone 
does  not  reduce  but  increases  the  power  of  the  north  part. 
Hence  if  a  loadstone  be  cut  and  divided  at  the  Arctic  circle, 
or  at  the  tropic  of  Cancer,  or  at  the  equator,  the  south  part 
does  not  so  powerfully  attract  at  its  pole  as  before  ;  for  a  new 
whole  arises  and  the  equator  leaves  its  former  place  and  ad- 
vances poleward,  because  of  the  division  of  the  stone.  In  the 
former  state,  inasmuch  as  the  opposite  part  of  the  stone  be- 
yond the  plane  of  the  equator  increases  the  mass,  it  also 
strengthens  the  verticity  and  the  force  .  and  the  movement 
toward  unition. 


ROTARY  NEEDLES  AND    THEIR  ADVANTAGES.         223 


CHAPTER  XVII. 

OF  THE  USE  OF  ROTARY  NEEDLES  AND  THEIR  ADVANTAGES  ; 
HOW  THE  DIRECTIVE  IRON  ROTARY  NEEDLES  OF  SUN- 
DAILS  AND  THE  NEEDLES  OF  THE  MARINER'S  COMPASS 
ARE  TO  BE  RUBBED  WITH  LOADSTONE  IN  ORDER  TO 
ACQUIRE  STRONGER  VERTICITY. 

Magnetized  versoriums  (or  magnetized  rotary  needles) 
serve  so  many  purposes  in  the  life  of  man,  that  it  will  not  be 
out  of  place  to  show  the  best  process  for  rubbing  and  magnet- 
ically exciting  them  and  the  proper  method  of  applying  the 
process.  With  the  aid  of  a  small  bar  of  iron  magnetically  pre- 
pared and  suspended  in  equilibrium,  rich  iron  ores  and  those 
containing  most  metal  are  recognized,  and  magnetic  stones, 
clays,  and  earths,  whether  crude  or  prepared,  are  distinguished. 
A  little  iron  bar — that  soul  of  the  mariner's  compass,  that 
wonderful  director  in  sea-voyages,  that  finger  of  God,  so  to 
speak — points  the  way  and  has  made  known  the  whole  circle 
of  earth,  unknown  for  so  many  ages.  Spaniards  (and  English- 
men too)  have  again  and  again  circumnavigated  the  whole 
globe  on  a  vast  circle  by  the  help  of  the  mariner's  compass. 
They  who  travel  on  land  or  who  remain  at  home  have  sun-dial 
horologes.  The  magnetic  needle  pursues  and  searches  for 
veins  of  iron  in  mines :  with  its  help  mines  are  driven  when 
cities  are  besieged  ;  cannons  and  military  engines  are  trained 
at  night  in  the  desired  directions.  The  needle  is  of  use  for  to- 
pography, for  determining  the  areas  and  position  of  buildings, 
and  in  constructing  underground  aqueducts.      On  it  depend 


224 


WILLIAM  GILBERT. 


the  instruments  invented  for  investigating  its  own  dip  and  its 
own  variation.  When  iron  is  to  be  quickened  by  the  loadstone, 
let  it  be  clean  and  neat,  not  disfigured  by  rust  or  dirt,  and  have 
it  of  the  best  steel.  Let  the  stone  be  wiped  dry  so  that  there 
shall  be  no  moisture,  and  scrape  it  gently  with  some  well- 
polished  iron  tool.  But  beating  it  with  a  hammer  is  of  no 
avail.  And  let  the  naked  iron  be  applied  to  the  naked  stone 
and  rubbed  at  it  in  such  a  way  that  they  may  come  into  closer 
contact — not  in  order  that  the  corporeal  matter  of  the  stone 
may  be  joined  to  the  stone  and  stick  to  it,  but  the  two  are 
slightly  worn  away  by  the  friction,  and  (useless  parts  being 
ground  off)  are  united  closely :  hence  arises  in  the  excited  iron 
a  grander  force.  In  the  figure,  A  shows  the  best  mode  of  ap- 
plying the  versorium  to  the  stone — its  point  touches  the  pole 
and  is  directed  toward  the  pole — B  is  a  passable  mode,  for 
though  it   is  at  a  Httle  distance  from  the  pole  it  is  directed 


toward  it ;  so,  too,  C  is  only  a  passable  mode,  the  point  being 
turned  away  from  the  pole  ;  Z>  is  a  worse  mode  on  account  of 
the  greater  distance  from  the  pole  ;  i^  is  a  bad  mode  because 
it  lies  on  a  parallel  across  the  stone  ;  the  magnetic  needle  L 


ROTARY  NEEDLES  AND    THEIR  ADVANTAGES.        225 

that  is  rubbed  on  the  equator  is  of  no  value  and  plainly  is  neg- 
ative and  forceless ;  the  oblique  indirect  mode  G  and  the 
oblique  indirect  averse  H  slxq  both  bad. 

The  purpose  of  all  this  is  to  show  the  different  powers  of  a 
globular  loadstone.  But  the  artificers  often  use  a  stone  rather 
tending  toward  the  conical  form,  and,  therefore,  more  power- 
ful, its  topmost  projection  being  the  pole,  at  which  they  rub 
the  needles.  Sometimes,  also,  the  stone  has  at  the  top  and 
above  the  very  pole  an  artificial  cap  or  snout  of  steel  to  give 
more  strength  ;  on  this  cap  iron  versoriums  are  rubbed,  and 
thereafter  they  turn  to  that  same  pole  as  though  they  had  been 
magnetized  at  that  part  without  the  cap. 

The  stone  should  be  of  good  size  and  strong ;  the  versorium, 
even  if  it  be  long,  must  be  pretty  thick,  not  too  thin,  with 
moderate-sized  point,  not  too  sharp,  though  the  energy  is  not 
in  the  point  itself  but  in  the  whole  needle.  Any  powerful, 
large  loadstone  serves  well  for  rubbing  versoriums,  though 
sometimes,  owing  to  its  powerfulness,  it  causes,  when  the 
needle  is  long,  some  dip  and  perturbation,  so  that  the  needle, 
that  before  friction  stood  in  equilibrium  in  the  plane  of  the 
horizon,  now,  after  friction  and  excitation,  dips  with  one  end 
as  low  as  the  fulcrum  on  which  it  is  supported  permits.  Hence 
in  the  case  of  a  long  versorium  the  end  that  is  to  be  north 
should  be,  before  friction,  a  little  lighter  than  the  other  end,  so 
that  it  may  remain  in  exact  equipoise  after  friction.  But  a 
versorium  so  prepared  performs  its  function  poorly  at  any  con-  * 
siderable  distance  from  the  equinoctial  circle. 

When  the  versorium  has  been  magnetized,  put  it  back  in 
its  box,  and  do  not  let  it  come  in  contact  with  other  magnetic 
bodies,  nor  remain  in  close  neighborhood  with  them,  lest  it 
become  unsteady  and  sluggish  through  the  action  of  opposite 
forces,  whether  potent  or  feeble.     And  if  you  rub  the  other 


226  WILLIAM  GILBERT. 

end  of  the  needle  at  the  opposite  pole  of  the  stone,  the  needle 
will  act  with  more  steadiness,  especially  if  it  be  rather  long. 
Iron  rubbed  with  loadstone  keeps  constant  and  strong,  even 
for  several  centuries,  the  magnetic  power  awakened  in  it,  if  it 
be  laid  in  the  natural  position,  meridionally,  not  on  a  parallel, 
and  is  not  spoilt  by  rust  or  any  external  ill  coming  from  the 
ambient  medium. 

Porta  seeks  amiss  a  ratio  between  loadstone  and  iron  :  a 
small  mass  of  iron,  saith  he,  cannot  hold  a  great  measure 
of  power,  for  it  is  wasted  by  the  mighty  energy  of  the  load- 
stone. Clearly,  the  iron  takes  to  the  full  its  own  virtue,  though 
it  weigh  only  one  scruple  and  the  mass  of  the  loadstone  more 
than  lOO  lbs.  It  is  vain  also  to  make  the  versorium  rather  flat 
at  the  end  that  is  rubbed  in  order  that  it  may  become  a  better 
and  stronger  magnetic  body,  and  that  it  may  better  seize  and 
hold  certain  magnetic  particles,  but  few  of  which  can  adhere 
to  a  sharp  point ;  for  it  was  Porta's  belief  that  the  energy  is 
transmitted  and  retained  by  adhesion  of  particles  of  the  load- 
stone, like  hairs,  whereas  these  particles  are  simply  scrapings 
detached  by  the  iron  from  the  softer  stone  ;  besides,  the  mag- 
netized iron  points  steadily  north  and  south  if,  after  friction,  it 
be  scoured  with  sand  or  emery  or  other  material,  and  even 
though  by  long-continued  friction  its  outer  parts  be  ground 
down  and  worn  away.  In  stroking  the  loadstone  with  a  ver- 
sorium each  stroke  should  terminate  at  one  end  of  the  verso- 
rium, else,  if  the  stroke  is  made  toward  the  middle,  a  less  degree 
of  verticity,  or  none  at  all,  or  very  little,  is  excited  in  the  iron. 
For  where  the  contact  ends  there  is  the  pole  and  the  point 
of  verticity.  To  produce  stronger  verticity  in  iron  by  friction 
*  with  a  loadstone,  it  is  necessary  in  northern  latitudes  to  turn  the 
loadstone's  true  north  pole  toward  the  zenith;  on  such  pole 
that  end  of  the  versorium  is  to  be  rubbed  which  afterward  will 


ROTARY  NEEDLES  AND    THEIR  ADVANTAGES.        22/ 

turn  to  the  earth's  north ;  the  other  end  of  the  versorium  must 
be  rubbed  on  the  south  pole  of  the  terrella  turned  toward  the 
earth ;  so  excited,  it  will  incline  to  the  south.  In  southern 
latitudes,  below  the  equator,  the  case  is  different,  and  the  cause 
of  the  difference  is  given  in  Book  II,  Chap.  34,  where  is  shown 
(by  means  of  a  combination  of  earth  and  terrella)  why  the  poles 
of  a  loadstone  are,  for  diverse  reasons,  one  stronger  than  the 
other. 

If  between  the  ends  of  two  loadstones  in  conjunction  and  * 
equal  in   power,  shape,  and   mass,  you   rub  a  versorium,  it 


acquires  no  property.  A,  B  are  two  loadstones  conjoined  nat- 
urally at  their  opposite  ends  ;  C,  the  point  of  a  versorium, " 
touched  simultaneously  by  both,  is  not  excited,  if  the  load- 
stones be  equal  (though  the  loadstones  are  connected  with  it 
in  the  natural  way);  but  if  the  loadstones  be  unequal,  force  is 
gained  from  the  stronger. 

In  magnetizing  a  versorium  with  a  loadstone  begin  at  its 
middle  and  so  draw  it  over  the  stone  that  one  end  quits  the 
stone  last ;  finally  let  the  application  be  continued  by  a  gentle 
stroking  of  the  stone  with  the  end  of  the  needle  for  a  while, 
say  one  or  two  minutes.  The  movement  from  middle  to  end 
must  not,  as  is  the  wont,  be  repeated,  for  so  the  verticity  is 
spoilt.  Some  delay  is  needed,  for  though  the  energy  is  infused 
and  the  iron  is  excited  instantaneously,  still  the  verticity  is 


228 


WILLIAM   GILBERT. 


more  steady  and  endures  more  surely  in  the  iron  when  the  ver- 
sorium  is  left  near  the  loadstone  and  abandoned  at  rest  for  a 
proper  length  of  time ;  although  an  armed  stone  lifts  a  greater 
weight  of  iron  than  an  unarmed,  still  a  versorium  is  not  more 
powerfully  magnetized  by  the  armed  than  by  the  unarmed 
stone.  Take  two  pieces  of  iron  wire,  of  equal  length,  cut  off 
the  same  coil  of  wire,  and  let  one  be  excited  by  the  armed  end, 
the  other  by  the  unarmed  end :  it  will  be  found  that  they  begin 
to  move  and  make  a  perceptible  inclination  toward  the  load- 
stone at  the  same  distances :  this  can  be  ascertained  by  meas- 
urement with  a  long  rod.  But  objects  powerfully  excited  turn 
quickly  to  the  pole,  those  that  are  feebly  excited  turn  slowly 
and  only  when  brought  nearer  :  the  experiment  is  made  in 
water  with  corks  of  equal  size. 


BOOK   IV. 


CHAPTER   I. 


OF     VARIATION. 


So  far  we  have  been  treating  of  direction  as  if  there  were 
no  such  thing  as  variation  ;  for  we  chose  to  have  variation  left 
out  and  disregarded  in  the  foregoing  natural  history,  just  as  if 
in  a  perfect  and  absolutely  spherical  terrestrial  globe  variation 
could  not  exist.  But  inasmuch  as  the  magnetic  direction  of 
the  earth,  through  some  fault  and  flaw,  does  depart  from  the 
right  track  and  the  meridian,  the  occult  and  hidden  cause  of 
variance  which  has  troubled  and  tormented,  but  to  none  effect, 
the  minds  of  many  has  to  be  brought  to  light  by  us  and 
demonstrated.  They  who  hitherto  have  written  of  the  mag- 
netic movements  have  recognized  no  difference  between  direc- 
tion and  variation,  but  hold  that  there  is  one  only  movement 
of  the  magnetized  needle.  But  the  true  direction  is  a  move- 
ment of  the  magnetic  body  to  the  true  meridian,  and  continu- 

22g 


230  WILLIAM  GILBERT. 

ance  therein,  with  the  ends  pointing  to  the  respective  poles. 
Yet  very  oft  it  happens,  afloat  and  ashore,  that  a  magnetic 
needle  does  not  look  toward  the  true  pole,  but  is  drawn  to  a 
point  in  the  horizon  nigh  to  the  meridian,  and  that  there  is  a 
deflection  not  only  of  the  needle  and  magnetized  iron  in  gen- 
eral and  of  the  mariner's  compass,  but  also  of  a  terrella  on  its 

*  float,  of  iron  ore  and  ironstone,  and  of  magnetic  clays  artifi- 
cially treated ;  for  they  often  look  with  their  poles  toward 
points  different  from  the  meridian.  The  variation,  then,  as 
observed  with  the  aid  of  instruments  or  of  the  mariner's  com- 
pass, is  an  arc  of  the  horizon  between  the  intersection  of  the 
horizon  by  the  meridian  and  the  term  of  the  deflection  on  the 
horizon,  or  the  range  of  deviation  of  the  magnetized  body. 
This  arc  varies  and  is  different  according  to  locality.^  So  the 
terminus  of  the  variation  is  commonly  assigned  to  a  great  circle 
— the  circle  of  variation,  as  it  is  called — and  a  magnetic  merid- 
ian passing  through  the  zenith  and  the  point  of  variation  on 
the  horizon. 

In  northern  terrestrial  latitudes  this  variation  takes  place 
either  in  the  direction  from  north  toward  east,  or  from  north 
toward  west ;  in  southern  latitudes,  in  like  manner,  it  is  from 
south  toward  east,  or  south  toward  west.     Hence  in  northern 

*  latitudes  we  must  heed  the  end  of  the  needle  that  tends  north, 
and  in  southern  latitudes  the  end  looking  south :  this  naviga- 


*  Gilbert  defines  variation  to  be  the  arc  intersected  between  the  point 
where  the  meridian  of  the  place  cuts  the  horizon  and  that  point  to  which  the 
magnetic  needle  looks  ;  the  length  of  this  arc  varying  with  the  place  of  observa- 
tion." ("  Nature  "  for  April  27,  1876,  page  523.)  The  variation  is  now  known 
by  scientific  writers  as  the  declination.  As  expressed  by  Commander  A.  W. 
Greely,  "  declination  is  the  variation  of  the  magnetic  meridian  from  the  geo- 
graphical meridian.  It  is  measured  by  the  angle  between  the  two  meridians, 
and  is  expressed  in  degrees  of  azimuth  from  zero  either  to  the  east  or  to  the  west 
of  the  true  north.  When  the  magnetic  north  is  west  of  the  true  north  it  is  west 
declination,  and  east  when  the  reverse  occurs." 


VARIATION.  231 

tors  and  sciolists  seldom  understand,  for  on  both  sides  of  the 
equator  they  note  only  the  north  point  terminal  of  the  com- 
pass, or  the  one  that  looks  north.  As  we  have  already  said, 
every  movement  of  loadstone  and  needle,  every  turn  and  dip, 
and  their  standing  still,  are  effects  of  the  magnetic  bodies 
themselves  and  of  the  earth,  mother  of  all,  which  is  the  fount 
and  source  and  producer  of  all  these  forces  and  properties. 
Thus,  then,  the  earth  is  the  cause  of  this  variation  and  ten- 
dence  to  a  different  point  in  the  horizon  ;  but  we  have  to 
inquire  further  how  and  by  what  potencies  it  acts. 

Here  we  must  first  reject  the  common  opinion  of  modern 
writers  concerning  magnetic  mountains  or  a  certain  magnetic 
rock  or  a  distant  phantom  pole  of  the  world  controlling  the 
movement  of  the  compass  or  of  the  versorium.  This  opinion 
Fracastorio  adopted  and  developed  after  it  had  been  broached 
by  others ;  but  it  does  not  agree  with  the  experiments  at  all. 
For,  if  it  were  correct,  in  different  places  on  land  and  sea  the 
variation  point  would  in  geometrical  ratio  change  to  east  or  to 
west,  and  the  versorium  would  always  regard  the  magnetic 
pole;  but  experience  teaches  that  there  is  no  determinate 
pole,  no  fixed  terminus  of  variation  in  the  globe.  For  the  arc 
of  variation  changes  in  different  ways  erratically,  so  that  in* 
different  meridians  and  even  in  the  same  meridian,  and  when, 
according  to  the  opinion  of  recent  writers,  the  magnetized 
needle  would  deviate  toward  east,  suddenly,  on  a  trifling 
change  of  place,  it  goes  from  north  toward  west,  as  in  the 
northern  regions  near  Nova  Zemlya  (Nova  Zembla)/  In 
southern  latitudes  also,  and  at  sea,  far  away  from  the  equator 
and  toward  the  Antarctic,  and  not  in  northern  latitudes  near 
those  magnetic  mountains,  is  variation  frequent  and  great. 


1  See  Book  IV,  Chap.  XVI. 


232  WILLIAM  GILBERT. 

But  still  more  vain  and  silly  are  the  imaginations  of  other 
writers — Cortesius,  for  example,  who  speaks  of  a  motive  force 
beyond  the  farthest  heavens ;  Marsilius  of  Ficino,  who  finds 
the  cause  of  variation  in  a  star  of  Ursa ;  Petrus  Peregrinus, 
who  finds  it  in  the  pole  of  the  world ;  Cardan,  referring  it  to 
the  rising  of  a  star  in  the  tail  of  Ursa ;  the  Frenchman  Bessard, 
to  the  pole  of  the  zodiac  ;  Livius  Sanutus,  to  a  certain  mag- 
netic meridian ;  Franciscus  Maurolycus,  to  a  magnetic  island  ; 
Scaliger,  to  the  heavens  and  to  mountains ;  the  Englishman 
Robert  Norman,  to  the  "  respective  point."  * 

Quitting,  therefore,  those  opinions  that  are  at  odds  with 
every-day  experience,  or  that  at  least  are  by  no  means  proven, 
let  us  look  for  the  true  cause  of  variation.  The  Great  Load- 
stone, or  the  terrestrial  globe,  gives,  as  I  have  said,  to  iron  a 
north  and  south  direction ;  magnetized  iron  readily  conforms 
itself  to  those  points.  But  as  the  globe  of  earth  is  at  its  sur- 
face broken  and  uneven,  marred  by  matters  of  diverse  nature, 
and  hath  elevated  and  convex  parts  that  rise  to  the  height  of 
some  miles  and  that  are  uniform  neither  in  matter  nor  in  con- 
stitution but  opposite  and  different,  it  comes  about  that  this 
entire  earth-energy  turns  magnetic  bodies  at  its  periphery 
toward  stronger  massive  magnetic  parts  that  are  more  power- 
ful and  that  stand  above  the  general  level.  Wherefore  at  the 
outmost  superficies  of  the  earth  magnetic  bodies  are  turned  a 
little  away  from  the  true  meridian.  And  since  the  earth's  sur- 
face is  diversified  by  elevations  of  land  and  depths  of  seas, 
great  continental  lands,  ocean,  and  seas  differing  in  every 
way, — while  the  force  that  produces  all  magnetic  movements 
comes  from  the  constant  magnetic  earth-substance,  which  is 
strongest  in  the  most   massive  continent  and  not  where  the 


1  See  Book  I,  Chap.  I;  Book  III,  Chap.  I;  Book  IV,  Chap.  VI. 


VARIA  TION.  233 

surface  is  water  or  fluid  or  unsettled, — it  follows  that  toward  a 
massive  body  of  land  or  continent  rising  to  some  height  in  any 
meridian  (passing  whether  through  islands  or  seas)  there  is  a 
measurable  magnetic  leaning  from  the  true  pole  toward  east  or 
west,  i.e.,  toward  the  more  powerful  or  higher  and  more  ele- 
vated magnetic  part  of  the  earth's  globe.'  For  as  the  earth's 
diameter  is  more  than  1700  German  miles,  these  continents 
may  rise  above  the  general  superficies  to  a  height  equal  to  the 
depth  of  the  ocean  bed,  or  more  than  four  miles,  and  yet  the 
earth  keep  the  spherical  shape,  albeit  slightly  uneven  at  the 
top.  For  this  reason  a  magnetic  body  under  the  action  of  the 
whole  earth  is  attracted  toward  a  great  elevated  mass  of  land 
as  toward  a  stronger  body,  so  far  as  the  perturbed  verticity 
permits  or  abdicates  its  right.  Yet  the  variation  takes  place 
not  so  much  because  of  these  elevated  but  less  perfect  parts  of 
the  earth  and  these  continental  lands,  as  because  of  the  inequal- 
ity of  the  magnetic  globe  and  of  the  true  earth-substance  which 
projects  farther  in  continents  than  beneath  sea-depths.  We 
have  therefore  to  inquire  how  the  demonstration  of  this  new 
natural  philosophy  may  be  drawn  from  unquestionable  experi- 
ments. 

From  the  coast  of  Guinea  to  Cape  Verde,  the  Canaries,  and 
the   frontier   of  the  empire   of   Morocco,    thence   along   the 

*  Gilbert  "refers  the  curvatures  of  the  isogenic  lines  to  the  configuration 
of  continents  and  the  relative  positions  of  sea  basins,  which  possess  a  weaker 
magnetic  force  than  the  solid  masses  rising  above  the  ocean."  He  considers 
"  that  the  inflections  of  the  lines  of  equal  declination  and  inclination  depend 
upon  the  distribution  of  mass,  the  configuration  of  continents,  or  the  form  and 
extent  of  the  deep  intervening  oceanic  basins.  It  is  difficult  to  connect  the 
periodic  variations  which  characterize  the  three  principal  forms  of  magnetic 
phenomena  (the  isoclinal,  isogonic,  and  isodynamic  lines)  with  this  rigid  sys- 
tem of  the  distribution  of  force  and  mass,  unless  we  represent  to  ourselves  the 
attractive  force  of  the  material  particles  modified  by  similar  periodic  changes  of 
temperature  in  the  interior  of  the  terrestrial  planet."  ("  Cosmos,"  1849,  Vol.  I, 
page  170;  Vol.  n,  pages  717,  718.) 


234  WILLIAM  GILBERT. 

coasts  of  Spain,  France,  England,  Holland,  Germany,  Den- 
mark, Norway,  the  land  on  the  right  and  to  the  east  is  all 
continent,  vast  regions  forming  one  mass ;  on  the  left,  immense 
seas  and  the  mighty  ocean  extend  far  and  wide':  now  we 
should  expect  that  (as  has  in  fact  been  observed  by  diligent 
investigators)  magnetic  bodies  would  deflect  a  little  eastward 
from  the  true  pole  toward  those  more  powerful  and  extraordi- 
nary elevations  of  the  terrestrial  globe.  Very  different  is  the 
case  on  the  east  coasts  of  North  America,  for,  from  the  region 
of  Florida  through  Virginia  and  Norumbega '  to  Cape  Race 
and  away  to  the  north,  the  needle  turns  to  the  west.  But  in 
the  mid  spaces,  so  to  speak,  for  example  in  the  western 
Azores,  it  regards  the  true  pole."  But  it  is  not  on  account  of 
that  meridian  or  of  the  coincidence  of  the  meridian  with  any 
magnetic  pole,  as  the  philosophastric  crew  suppose,  that  a 
magnetic  body  turns  in  like  manner  to  the  same  regions  of  the 
world ;  neither  does  the  variation  take  place  along  the  entire 

*  meridian,  for  on  the  same  meridian  near  Brazil  the  case  is  very 
different,  as  later  we  will  show. 

Other  things  equal,  variation  is  less  along  the  equator, 
greater    in    high    latitude,    save    quite    nigh   the   very    pole. 

*  Hence  it  is  greater  off  the  coast  of  Norway  and  Holland  than 
off  Morocco  or  Guinea ;  greater,  too,  at  Cape  Race  than  in  the 

^Norumbega,  "the  lost  city  of  New  England,"  was  called  Arambec,  or 
"Arambe"  in  1523,  "Aranbega"  in  1529,  "  Norumbega"  in  1539,  and,  sub- 
sequently, "  Norumbdega,"  "  Narembegue."  Norumbega,  in  the  Indian 
tongue,  means  the  place  of  a  fine  city.  Its  site  was  indicated  as  on  the  bank  of 
the  Penobscot,  the  province  of  that  name  extending  from  the  Kennebec  River 
to  the  St.  Croix  River  in  that  section  of  the  country  which  afterwards  became 
the  State  of  Maine.  (See  "  Magazine  of  Am.  Hist."  for  1877,  pages  14,  321, 
and  for  1886,  page  291,  "  New  England's  lost  city  found  ";  also,  "  Antiquitates 
Americanse,"  Roy.  Soc.  of  Copenhagen;  Lang's  "Sagas  of  the  Kings  of 
Norway;  Shea's  "Catholic  Church  in  Colonial  Days;"  Horsford,  "Cabot's 
Landfall  in  1497  and  the  site  of  Norumbega.") 

*  Humboldt,  "  Cosmos,"  London  1849,  Vol.  I,  page  175,  note. 


VARIATION  IS  DUE    TO  EARTH'S  ELEVATIONS.        235 

ports  of  Norumbega  or  of  Virginia.  In  the  Guinea  littoral, 
the  magnetized  needle  inclines  to  the  east  one-third  part  of  a 
point ;  in  the  Cape  Verde  Islands  two  thirds ;  in  England,  at 
the  mouth  of  the  Thames,  one  point :  the  higher  the  latitude 
the  stronger  the  moving  force,  and  the  masses  of  land  toward 
the  pole  exert  most  influence :  all  this  is  easily  seen  in  a  ter- 
rella.  For  just  as,  when  the  direction  is  true,  magnetic  bodies 
tend  toward  the  pole  (i.e.,  the  greater  force  and  the  entire  earth 
co-operating),  so  do  they  tend  a  little  toward  the  more  power- 
ful elevated  parts  under  the  action  of  the  whole  and  in  virtue 
of  the  concurrent  action  of  their  iron/ 


CHAPTER   II. 

THAT  VARIATION  IS  DUE  TO   INEQUALITY  AMONG  THE 
earth's   ELEVATIONS. 

This  very  thing  is  clearly  demonstrated  on  the  terrella 
thus :  take  a  spherical  loadstone  imperfect  in  any  part  or  de- 
cayed (I  once  had  such  a  stone  crumbled  away  at  a  part  of  its 
surface  and  so  having  a  depression  comparable  to  the  Atlantic 
sea  or  great  ocean);  lay  on  it  bits  of  iron  wire  two  barley- 
corns in  length,  as  in  the  figure.  AB  is  a  terrella  imperfect  in 
parts  and  of  unequal  power  on  the  circumference  ;  the  needles 
E,  F  do  not  vary  but  regard  the  pole  straight,  for  they  are 
placed  in  the  middle  of  the  sound  and  strong  part  of  the  ter- 
rella at  a  distance  from  the  decayed  part :  the  surface  that  is 

'  Ath.  Kircheri,  Magnes  ;  sive  de  arte  magnetica,  1643,  Lib.  II,  Pars.  V,  page 
410. 


236 


WILLIAM  GILBERT. 


dotted  and  that  is  marked  with  cross-lines  is  weaker.  Neither 
does  the  needle  O  vary  because  it  is  in  the  middle  line  of  the 
decayed  part,  but  turns  to  the  pole  just  as  off  the  western 
Azores.    H  and  L  vary,   for  they  incline  toward  the  sound 


parts.  And  as  this  is  shown  on  a  terrella  whose  surface  has 
sensible  imperfections,  so,  too,  in  terrellas  that  are  whole  and 
perfect,  for  often  one  part  of  a  stone  is  of  greater  strength  on 
the  outside  than  another,  though  no  difference  is  plain  to 
sense.  With  such  a  terrella  variation  is  demonstrated  and  the 
♦strong  points  are  discovered  in  the  following  way  :  Here  A  is 
the  pole,  B  the  place  of  variation,  C  the  more  powerful  region. 
The  horizontal  needle  at  B  varies  from  the  pole  (7-ward.  So 
is  the  variation  shown  and  the  regions  of  greater  force  recog- 
nized. The  more  powerful  surface  is  found  also  by  means  of 
a  slender  iron  wire  two  barley-corns  long  :  for  though  it  will 
stand  upright  on  the  pole  of  the  terrella  and  in  other  parts 


VARIATION  IS  DUE    TO  EARTH'S  ELEVATIONS.       237 

will  lean  toward  the  equator,  still  if  on  the  same  parallel  circle 
it  stands  more  nearly  erect  at  one  point  than  at  another,  the 
terrella's  surface  has  more  power  where  the  needle  is  the  more 


erect ;  and  also  when  a  piece  of  iron  wire  laid  on  the  pole  in- 
clines more  to  one  side  than  the  other.     For  experiment  take 


a  piece  of  iron  wire  three  finger-widths  long,  resting  on  the 
pole  A  so  that  its  middle  lies  over  the  pole.  One  of  the  ends 
turns  toward  C  and  will  not  rest  in  position  toward  B ;  yet,  in 
a  terrella  that  is  flawless  and  even  all  over,  it  will  be  at  rest  on 


238 


WILLIAM  GILBERT. 


the  pole  no  matter  toward  what  point  of  the  equator  it  be 
♦directed.     Or  make  another  experiment  :  Suppose  two  merid- 
ians meeting  at  the  poles  A,B  m.  equal  arcs  DA  and  CA  ;  at 


their  extremities  D,  and  C,  let  pieces  of  iron  wire  be  reared  :  at 
D  (which  is  the  region  of  greater  force)  the  wire  will  be  reared 
more  near  perpendicular  than  at  C,  the  region  of  less  force. 
Thus  can  we  discern  the  stronger  and  more  powerful  part  of  a 
loadstone,  else  not  recognizable  by  the  senses.  In  a  terrella 
that  is  perfect,  even,  and  alike  in  all  its  parts,  there  is  at  equal 
distances  from  the  pole  no  variation. 

Variation  may  be  shown  by  means  of  a  terrella  having  a 


onsiderable  part  of  its  surface  projecting  a  little  above  the 
rest :  such  terrella,  though  not  decayed  nor  spoilt,  attracts  out 


VARIATION  IS  DUE    TO  EARTH'S  ELEVATIONS.       239 

of  the  true  direction,  its  whole  mass  operating.  The  figure 
shows  a  terrella  with  uneven  surface.  The  demonstration  is* 
made  with  small  bars  or  short  needles  placed  on  the  terrella  : 
they  turn  from  the  terrella  toward  the  projecting  mass  and 
the  great  eminences.  In  this  way  is  verticity  disturbed  on  the 
earth  by  the  great  continents  which  mostly  rise  above  the 
beds  of  the  seas  and  which  at  times  cause  the  needle  to  devi- 


ate from  the  straight  track,  i.e.,  from  the  true  meridian.  The 
tip  of  the  versorium  A  does  not  point  toward  the  pole  P  if 
there  be  a  large  projection  B  on  the  terrella  ;  so,  too,  the 
point  C  varies  from  the  pole  because  of  the  projection  F. 
Midway  between  the  two  eminences,  the  needle  G  points  to 
the  true  pole,  because,  being  equidistant  from  both  projections 
B  and  F,  it  deviates  to  neither  but  keeps  the  true  meridian. 


240  WILLIAM  GILBERT. 

particularly  when  the  energy  of  the  projections  is  equal.  But 
elsewhere,  at  iV,  the  needle  varies  from  the  pole  M  toward  the 
eminence  H,  nor  is  hindered  nor  stayed  nor  checked  by  the 
small  eminence  D  on  the  terrella,  which  is  like  some  island  of 
the  earth  in  the  ocean.     But  L  unhindered  tends  poleward. 

In  another  mode  may  variation  be  shown,  whether  in  a 
terrella  or  on  the  earth.  Let  A  be  the  earth's  pole ;  B  its 
equator  ;  C  a  parallel  circle  at  latitude  30  degrees ;  D  an  emi- 
nence reaching  poleward  ;  E  another  eminence  stretching  from 
the  pole  equatorward.  Evidently  the  versorium  F  in  the 
middle  line  of  D  does  not  vary ;  but  G  deflects  very  much,  C 
very  little  as  being  more  remote  from  D.  So,  too,  the  needle 
/,  placed  directly  toward  E,  does  not  deflect  from  the  pole : 
but  L  and  M  turn  from  the  pole  toward  the  eminence  E. 


CHAPTER  III. 

VARIATION  IS  CONSTANT  AT  A   CiiVEN  PLACE.' 

As  the  needle  hath  ever  inclined  toward  east  or  toward 
west,  so  even  now  does  the  arc  of  variation  continue  to  be  the 
same  in  whatever  place  or  region,  be  it  sea  or  continent ;  so, 

>  Henry  Gellibrand,  English  mathematician,  professor  of  geometry  at 
Gresham  College,  discovered,  1633-1635,  the  secular  variation  of  the  declination. 
In  the  words  of  Dr.  Whewell  ("  Hist,  of  the  Ind.  Sciences,"  1859,  Vol.  II,  page 
219)  :  "  Gellibrand  discovered  that  the  variation  is  not  constant,  as  Gilbert  im- 
agined, but  that  in  London  it  had  diminished  from  eleven  degrees  east  in  1580 
to  four  degrees  in  1633.  Since  that  time  the  variation  has  become  more  and 
more  westerly;  it  is  now  about  twenty-five  degrees  west,  and  the  needle  is  sup- 
posed to  have  begun  to  travel  eastward  again. 

It  may  be  added  that  the  diurnal  variation  was  subsequently  found  by 
George  Graham,  during  the  year  1722,  whilst  the  annual  variation  was  made 
known  by  Jean  Jacques  Dominique  Cassini  between  1782  and  1791. 


VARIATION  IS  CONSTANT  AT  A    GIVEN  PLACE.       24I 

too,  will  it  be  forevermore  unchanging,  save  there  should  be  a 
great  break-up  of  a  continent  and  annihilation  of  countries,  as 
of  the  region  Atlantis,  whereof  Plato  and  ancient  writers  tell. 
The  constancy  of  the  variation  and  the  regard  of  the  verso- 
rium  toward  a  fixed  point  of  the  horizon  in  each  region  is 
shown  by  laying  a  very  small  versorium  on  a  terrella  of  uneven 
surface :  the  needle  always  diverges  from  the  meridian  over 
an  equal  arc.  It  is  shown  also  by  the  inclination  of  the  needle 
toward  a  second  loadstone,  though  in  truth  this  is  done  by  a 
changed  direction  of  all  within  the  earth  and  the  terrella. 
Lay  upon  a  plane  surface  a  versorium  with  its  point  looking 


toward  A,  north;  bring  alongside  the  loadstone  B,  at  such 
distance  as  to  make  the  versorium  turn  to  C  and  no  further. 
Move  the  needle  of  the  versorium  as  often  as  you  will  (yet 
without  stirring  either  its  case  or  the  loadstone)  and  the 
needle  will  ever  surely  return  to  the  point  C.  Thus  if  you  so 
hold  the  stone  as  to  make  the  needle  turn  to  E,  its  point  ever 
returns  to  E  and  not  to  any  other  point  of  the  compass.  Just 
so,  by  reason  of  the  position  of  countries  and  the  differing 
nature  of  the  uppermost  parts  of  the  earth's  globe  (certain 
more  magnetic  projections  of  the  terrestrial  sphere  prevailincj). 


242  WILLIAM  GILBERT. 

variation  is  ever  fixed  in  a  given  place,  but  it  differs  and  is 
unequal  between  one  place  and  another,  for  the  true  and  polar 
direction,  having  its  birth  in  the  entire  globe  of  earth,  is 
slightly  diverted  toward  particular  eminences  of  great  mag- 
netic force  on  the  broken  surface. 


CHAPTER  IV. 

THE    ARC    OF    VARIATION  DOES    NOT  DIFFER  ACCORDING  TO 
DISTANCE   BETWEEN   PLACES. 

On  the  broad  ocean,  while  a  ship  is  borne  by  favoring  wind 
along  the  same  parallel,  if  the  variation  be  reduced  just  one 
degree  in  a  voyage  of  lOO  miles,  it  does  not  follow  that  the 
next  100  miles  will  reduce  it  another  degree.  For  the  needle 
varies  according  to  the  position  and  conformation  of  the  land 
and  the  magnetic  force ;  also  according  to  distance.  For 
example,  when  a  ship  from  the  Scilly  Islands  bound  for  New- 
foundland has  proceeded  so  far  that  the  compass  points  to 
the  true  magnetic  pole,  then,  as  she  sails  on,  the  borrholybic 
variation  begins,  but  faintly  and  with  small  divergence.  But 
after  a  while  the  arc  increases  in  a  higher  ratio  as  equal  distances 
are  traversed,  till  the  ship  comes  nigh  the  continent,  when  the 
variation  is  very  great.  Yet  before  she  comes  quite  to  land 
or  enters  port,  while  at  some  distance  away,  the  arc  is  again 
lessened  a  little.  But  if  the  ship  in  her  course  departs  much 
*from  that  parallel,  either  to  north  or  south,  the  needle  will 
vary  more  or  less  according  to  the  position  of  the  land  and  the 
latitude  of  the  region ;  for,  other  things  equal,  the  higher  the 
latitude  the  greater  the  variation. 


VARIATION  NOT  ALTERED  BY  AN  OCEAN  ISLAND.     243 


CHAPTER  V. 

AN    ISLAND    IN    OCEAN  DOES    NOT  ALTER    THE    VARIATION; 
NEITHER  DO   MINES   OF   LOADSTONE. 

Islands,  albeit  they  are  more  magnetic  than  the  seas,  still 
do  not  alter  magnetic  direction  nor  variation.  For  direction 
being  a  movement  produced  by  the  energy  of  the  entire  earth, 
and  not  due  to  the  attractive  force  of  any  prominence  but  to 
the  controlling  power  and  verticity  of  the  whole  mass,  there- 
fore variation  (which  is  a  perturbation  of  the  directive  force), 
is  a  wandering  from  the  true  verticity  and  arises  out  of  the 
great  inequalities  of  the  earth,  by  reason  of  which  the  earth 
itself,  when  very  large  and  powerful  magnetic  bodies  are 
present,  has  but  little  power  of  turning  away  magnetic  bodies 
that  revolve  freely.  As  for  the  wonders  that  some  do 
report  about  the  island  Elba :  loadstones  do  there  abound, 
but,  nevertheless,  the  versorium  (or  the  mariner's  compass) 
makes  no  special  inclination  toward  it  when  ships  sail  by  in  the 
Tyrrhenian  Sea.^  The  reasons  already  given  sufficiently 
account  for  this ;  but,  furthermore,  a  reason  may  be  found 
in  the  fact  that  the  energy  of  minor  loadstones  reaches  of  it- 
self but  little  beyond  their  own  site ;  for  variation  is  not  pro- 
duced by  a  pulling  to,  as  they  would  make  it  who  have 
thought  out  magnetic  poles.  Besides,  mines  of  loadstone  are 
only  agnate,  not  innate,  in  the  true  earth-substance,  and,  there- 
fore, the  globe  as  a  whole  does  not  heed  them  ;  neither  are 
magnetic  bodies  borne  toward  them,  as  is  proved  in  the  dia- 
gram of  prominences. 

^  See  note  relative  to  Elba,  Book  I,  Chap.  VIII. 


244  WILLIAM  GILBERT. 


CHAPTER  VI. 

THAT  VARIATION  AND  DIRECTION  ARE  PRODUCED  BY  THE 
CONTROLLING  FORCE  OF  THE  EARTH  AND  THE  ROTA- 
TORY MAGNETIC  NATURE,  NOT  BY  AN  ATTRACTION  OR  A 
COITION,  OR  BY  OTHER  OCCULT  CAUSE. 

Inasmuch  as  the  loadstone  is  deemed  by  the  philoso- 
phizers  of  the  vulgar  sort  to  seize  and  snatch  objects  away,  as  it 
were,  and  pretenders  to  science  have,  in  fact,  noticed  no  other 
properties  save  this  much-lauded  force  of  attraction,  therefore 
they  have  supposed  that  the  whole  movement  to  north  and 
south  is  produced  by  some  natural  force  soliciting  bodies.  But 
the  Englishman  Robert  Norman  first  strove  to  show  that  this 
is  not  done  by  attraction  ;  he,  therefore,  originated  the  idea 
of  the  "  respective  point "  looking,  as  it  were,  toward  hidden 
principles,  and  held  that  toward  this  the  magnetized  needle 
ever  turns,  and  not  toward  any  attractional  point ;  but  he  was 
greatly  in  error,  albeit  he  exploded  the  ancient  false  opinion 
about  attraction.  Norman  proves  his  theory  as  follows :  Take 
a  round  vessel  full  of  water ;  on  the  mid  surface  of  the  water 
float  a  small  bit  of  iron  wire  supported  by  just  so  much  cork 
as  will  keep  it  afloat  while  the  water  is  in  equilibrium ;  the 
wire  must  have  been  first  magnetized  so  as  to  show  plainly  the 
variation  point  D.  Let  it  remain  in  the  water  for  a  while. 
Clearly  the  wire  with,  its  cork  does  not  move  toward  the  rim 
D  of  the  vessel,  as  it  would  do  if  attraction  came  to  the  iron 
from  D,  and  the  cork  would  move  from  its  place.  This  asser- 
tion of  the  Englishman  Robert  Norman  is  demonstrable,  and 


VARIA  TION  AND   DIRECTION. 


245 


it  does  seem  to  do  away  with  attraction,  inasmuch  as  the  iron 
remains  in  the  still  water  both  in  the  direction  toward  the 
very  pole  (if  the  direction  be  true)  and  in  variation  and  irreg- 
ular direction  ;  and  it  revolves  on  its  iron  centre,  and  is  not 
borne  toward  the  vessel's  rim.  Yet  the  direction  is  not  pro- 
duced by  attraction,  but  by  a  disposing  and  conversory  power 


existing  in  the  earth  as  a  whole,  not  in  a  pole  or  any  attra- 
hent  part  of  the  stone,  neither  in  any  mass  projecting  beyond 
the  circle  of  the  periphery,  so  that  the  variation  should  result 
because  of  the  attraction  of  that  mass.  Besides,  the  directive 
force  of  the  stone  and  of  iron,  and  their  natural  power  of  re- 
volving on  their  centre,  produce  the  movement  of  direction  and 
of  collimation,  in  which  is  included  also  the  motion  of  dip  or 
inclination  {declinationis).  Nor  does  the  earth's  pole  attract  as 
though  the  force  of  the  globe  resided  in  the  pole  only :  the 
magnetic  force  exists  in  the  whole,  but  in  the  pole  it  is  pre- 
eminent and  surpassing.  Therefore  that  the  cork  abides 
quietly  in  the  midst,  and  that  the  magnetic  needle  does  not 
move  toward  the  rim  of  the  vessel,  is  a  fact  in  accord  and 
agreement  with  the  loadstone's  nature,  as  is  shown  with  the 
aid  of  a  terrella.     Here  a  little  iron  bar, placed  on  the  stone  at* 


246  WILLIAM  GILBERT, 

C,  clings  there,  nor  is  it  pulled  farther  away  by  the  pole  A  or 
by  the  parts  near  the  pole.  So,  too,  it  continues  at  D  and 
takes  direction  toward  the  pole  A,  but  it  sticks  at  D,  and  dips 


also  toward  D  in  virtue  of  its  power  of  rotation  whereby  it 
conforms  itself  to  the  terrella.  On  this  point  we  shall  treat 
further  when  we  consider  inclination  or  the  dip  of  the  com- 
pass. 


CHAPTER  VII. 

WHY  THE  VARIATION  DUE  TO  THIS  LATERAL  CAUSE  IS  NOT 
GREATER  THAN  HITHERTO  IT  HAS  BEEN  OBSERVED  TO 
BE,  SELDOM  APPEARING  TO  AMOUNT  TO  TWO  POINTS 
OF  THE  COMPASS,  EXCEPT  NEAR  THE    POLE. 

The  earth,  by  reason  of  lateral  elevations  of  the  more 
energic  globe,  causes  iron  and  loadstone  to  diverge  a  few 
degrees  from  the  true  pole  or  true  meridian.  For  example, 
here  in  England,  at  London,  it  varies  1 1^  degrees ;  in  some 
other  places  the  variation  is  somewhat  greater,  yet  in  no  region 
does  the  end  of  the  needle  diverge  very  many  degrees  more 
from  the  meridian.'    For  as  the  needle  always  gets  its  direction 

1  Consult  Cabeo,  Philos,  Magn.,  Ferrara  1629,  Lib.  I,  Cap.  XVI. 


WHY   VARIATION  IS  NOT  GREATER    THAN  HITHERTO.    247 


from  the  true  verticity  of  the  earth,  so  the  polar  nature  of  a 
continent  tends  poleward,  even 
as  does  that  of  the  whole  globe 
of  earth  ;  and  though  the  mass  of 
a  continent  may  turn  magnetic 
bodies  away  from  the  meridian, 
still  the  verticity  of  that  same 
land  (as  of  the  whole  earth  also) 
controls  and  directs  those  bodies 
so  that  they  shall  not  turn  east- 
ward in  too  large  an  arc.  It  were 
not  easy  to  determine  according 
to  any  general  method  how  great 
the  arc  of  variation  is  in  every 
place,  nor  how  many  degrees  and 
minutes  it  covers  on  the  horizon, 
because  it  becomes  greater  or 
less  according  to  divers  causes. 
For  we  must  take  account  of 
the  force  of  true  verticity  of 
each  place  and  of  the  elevated 
regions,  also  of  the  distances 
of  those  regions  from  the  place 
under  consideration  and  from  the 
world's  poles ;  and  these  distances 
are  to  be  compared — a  thing  that 
cannot  be  done  with  precision. 
Still,  by  our  method,  the  variation 
is  ascertained  in  such  way  that  no 
serious  error  is  left  to  perturb  the 
course  of  a  sea-voyage.  Were  the 
positions   of  masses  of  land  uniform,  if   the   land   lay  on   a 


248  WILLIAM  GILBERT. 

meridian  line,  and  did  not  present  a  broken  and  indented 
contour,  the  variations  near  the  land  would  be  without  com- 
plexity, as  in  the  figure. 

This  is  demonstrated  with  the  aid  of  a  long  loadstone 
whose  poles  are  at  the  ends  A,  B :  the  middle  of  the  load- 
stone and  the  equinoctial  is  CD ;  and  the  lines  GH  and  EF 
are  meridians  on  which  are  arranged  versoriums,  the  deviations 
of  which  are  greater  the  greater  their  distance  from  the 
equator.  But  the  inequalities  of  the  seaboard  parts  of  the 
habitable  globe,  the  great  promontories,  the  wide  gulfs,  the 
mountainous  and  the  more  elevated  regions,  and  the  more 
uneven  and  precipitous  regions  make  the  variations  more 
difificult  of  determination,  and  in  high  latitudes  less  certain 
and  more  irregular. 


CHAPTER   VIII. 

OF  THE  CONSTRUCTION  OF  THE  COMMON  MARINER'S  COM- 
PASS, AND  OF  THE  DIFFERENT  COMPASSES  OF  VARIOUS 
NATIONS. 

In  a  round  wooden  box  (bowl),  having  its  top  covered  over 
with  glass,  a  fly-card  (versorium)  rests  on  a  pretty  long  pin 
fixed  in  the  middle.  The  glass  cover  keeps  out  wind  and 
draughts  of  air  produced  by  outer  causes.  All  that  is  within  can 
be  distinctly  seen  through  the  glass.  The  versorium  (rotating 
part)  is  circular,  made  of  light  material,  as  pasteboard,  to  the 
under  side  of  which  is  attached  the  magnetized  iron  or  needle. 
On  the  upper  side  32  spaces  (points  as  they  are  called)  are 
distributed  to  as  many  mathematical  intervals  in  the  horizon. 


THE   CONSTRUCTION  OF  COMPASSES.  249 

or  winds,  which  are  distinguished  by  certain  marks  and  by  a 
lily  (^fleur-de-lis)  indicating  the  north.  The  compass-box  is 
suspended  in  equilibrium  in  the  plane  of  the  horizon,  within  a 
ring  of  brass,  which  is  also  pivoted  (equilibrated)  in  another 
ring  suspended  in  a  roomy  stand,  a  leaden  weight  being 
attached  to  the  box  so  that  it  shall  remain  in  the  plane  of  the 
horizon  though  the  ship  may  be  tossed  by  the  sea  in'  all  direc- 
tions. There  are  either  two  magnetized-iron  bars  (with  ends 
united)  or  one  piece  of  a  rather  oval  shape  with  the  ends  pro- 
jecting :  this  style  is  the  surer  and  quicker  of  the  two  in 
performing  its  function/  This  is  to  be  so  fitted  to  the  paste- 
board disk  (or  card  of  the  compass)  that  the  centre  of  the  disk 
shall  be  in  the  middle  of  the  magnetized  iron.  But  as  varia- 
tion begins  in  the  horizon  from  the  point  where  the  meridian 
intersects  it  at  right  angles,  therefore,  on  account  of  the 
variation,  instrument-makers  in  different  countries  and  cities 
inscribe  the  compass  variously,  and  have  different  ways  of 
attaching  the  magnetized  iron  to  the  card  whereon  are  marked 
the  bounds  of  the  32  spaces  or  points. 

There  are  in  general  use  in  Europe  four  different  con- 
structions and  forms  of  compass.  First,  the  form  adopted 
throughout  the  Mediterranean,  and  in  Sicily,  Genoa,  and  the 
Venetian  republic.  In  all  of  these  compasses  the  pieces  of 
iron  are  so  attached  beneath  to  the  rotating  card  that  (where 


'  This  opinion  of  Gilbert's  is  not  borne  out  by  advanced  knowledge  of  the 
laws  of  magnetization,  which  shows  that  the  oval  ring  needle  cannot  be  trusted 
to  for  keeping  its  magnetic  axis  securely  in  a  constant  direction  under  whatever 
disturbing  influence  it  may  be  subjected  to  as  does  a  thin  rod  or  bar.  The 
oval  form  was  authoritatively  condemned  on  this  account  by  the  British  Admi- 
ralty Committee  of  1837,  who  found  the  theoretical  objection  amply  confirmed 
by  experience.  They  actually  found  compasses  of  this  pattern,  which  had  been 
in  use  for  some  time  at  sea,  presenting  errors  of  as  much  as  three  degrees  on 
account  of  the  displacement  of  the  magnetization  in  the  substance  of  the  needle. 
(Sir  Wm.  Thomson,  "  Good  Words  "  for  1879,  page  445.) 


2SO  WILLIAM  GILBERT, 

there  is  no  variation)  they  turn  to  the  true  points  of  north 
and  south.  Hence  the  mark  for  north,  designated  by  a  lily, 
always  indicates  exactly  the  point  of  variation :  for  the  point 
of  the  lily  on  the  card,  together  with  the  ends  of  the  pieces  of 
magnetized  iron  beneath,  come  to  a  standstill  at  the  point  of 
variation.  Another  form  of  compass  is  that  of  Dantzic,  em- 
ployed in  the  Baltic  Sea  and  in  the  Netherlands.  Here  the 
magnetized  iron  underneath  diverges  three  fourths  of  one 
point  eastward  from  the  lily ;  for  a  voyage  to  Russia  the 
divergence  (recognized  difference)  is  two  thirds.  But  the 
compasses  made  at  Seville,  Lisbon,  Rochelle,  Bordeaux, 
Rouen,  as  well  as  throughout  all  England,  have  an  interval  of 
one  half  of  a  point. 

Out  of  these  differences  have  grown  very  serious  errors  in 
seafaring  and  in  the  science  of  navigation.  For,  after  the 
directional  positions  of  sea-coasts,  of  promontories,  ports, 
islands,  have  been  found  by  the  aid  of  the  compass,  and  the 
tides  of  the  seas  or  the  times  of  full  sea  have  been  determined 
from  the  moon's  position  above  one  or  another  point  of  the 
compass  (as  the  phrase  is),  we  have  still  to  inquire  in  what 
country  or  according  to  what  country's  usage  the  compass 
was  constructed  by  which  the  directions  of  said  places  and  the 
times  of  the  marine  tides  were  observed  and  determined.  For 
the  mariner,  who,  using  British  compass,  should  follow  the 
directions  of  the  Mediterranean  marine  charts,  must  needs 
stray  far  from  his  true  course ;  so,  one  who  should  use  an 
Italian  compass  in  the  North  Sea,  the  German  Sea,  or  the 
Baltic,  in  connection  with  the  marine  charts  commonly  used  in 
those  parts,  would  oft  stray  from  the  right  direction.  These 
differences  were  introduced  by  reason  of  the  unlike  variations, 
that  navigators  might  escape  grave  errors  in  those  parts  of  the 
world.    Yet  Petrus  Nonius  seeks  the  meridian  with  a  mariner's 


CAN  LONGITUDE  BE  FOUND  FROM   VARIATION?      2$ I 

compass  or  versorium  (the  Spaniards  call  it  a  needle),  taking  no 
account  of  variation  ;  and  he  brings  forward  many  geometric 
proofs  that  rest  on  utterly  vicious  foundations :  for  he  had 
small  acquaintance  or  experience  of  things  magnetic.  In  like 
manner  Pedro  de  Medina,  who  does  not  accept  variation,* 
has  with  many  errors  disgraced  the  art  of  navigation. 


CHAPTER  IX. 

WHETHER   TERRESTRIAL    LONGITUDE    CAN    BE    FOUND    FROM 

VARIATION. 

That  were  a  welcome  service  to  mariners  and  would 
advance  geography  very  much.  But  Porta  (Book  VII,  Chap. 
38)  is  deluded  by  a  vain  hope  and  by  a  baseless  theory.  For 
he  thinks  that,  in  moving  along  a  meridian,  the  needle  observes 
order  and  proportion,  so  that  the  nearer  it  is  to  east  the  more 
it  will  deviate  eastward,  and,  according  as  you  advance  west, 
the  needle  takes  a  westerly  direction :  all  of  which  is  false  as 
false  can  be.  Porta  thinks  he  has  found  a  true  index  of 
longitude ;  but  he  is  mistaken.  Taking,  however,  and  assum- 
ing for  true  these  premises,  he  constructs  a  large  compass 
showing  degrees  and  minutes  for  observing  these  proportional 
changes  of  the  needle.  But  his  principles  are  erroneous  and 
illogically  taken  and  very  poorly  studied  ;  for  a  versorium  does 
not  vary  more  to  the  east  because  it  is  carried  to  the  east ;  and 
though   in   the   countries   of   western    Europe   and   the   seas 

'  Pedro  de  Medina,  Arte  de  Navegar,  Valladolid  1545  (Ronalds,  page  341). 
Consult  L' arte  del  Navegar,  Dottor  M.  Pietro  da  Medina,  Vinetia  1555,  Libro 
Sesto,  "Delia  Aguggia,  over  bossolo  da  navegar,"  pages  cviii-cxvi. 


252  WILLIAM  GILBERT. 

adjoining  the  variation  is  to  the  east,  and  beyond  the  Azores 
it  is  changed  a  little  toward  the  west,  nevertheless  variation  is 
in  divers  ways  ever  uncertain,  both  because  of  latitude  and 
longitude  and  because  of  approach  to  great  masses  of  land, 
also  because  of  the  altitude  of  dominant  terrestrial  elevation  ; 
but  it  does  not  follow  the  rule  of  any  meridian,  as  we  have 
already  shown.  Livius  Sanutus  sorely  tortures  himself  and 
his  readers  with  like  vanities.  As  for  the  opinion  of  the 
common  run  of  philosophizers  and  mariners,  that  the  meridian 
which  passes  through  the  Azores  is  the  limit  of  variation,  so 
that  on  the  opposite  side  of  that  meridian  a  magnetic  body 
will  point  to  the  poles  exactly  as  at  the  Azores — an  opinion 
held  also  by  Joannes  Baptista  Benedictus  and  sundry  other 
writers  on  the  art  of  navigation — it  is  in  no  wise  true. 
Stevinus  (quoted  by  Hugo  Grotius),  in  his  Portuum  Invenien- 
darum  Rationed  distinguishes  variation  according  to  meridians. 
"In  the  island  Corvo,"*  says  he,  "the  magnetic  pointer 
indicates  the  true  north,^  but  the  farther  one  advances  thence 
toward   the  east  the   more  will  he  see   the  needle  'easting' 


'  Simon  Stevinus,  Portuum  Investigandorum  Ratio,  Leyden  1599.  This 
was  printed  in  English,  the  same  year,  by  the  celebrated  mathematician, 
Edward  Wright,  who  afterwards  attached  it  to  the  third  edition  of  his  "  Cer- 
taine  errors  in  navigation  detected  and  corrected"  (Engl.  Cycl.,  "Biography," 
Vol.  VI.  page  834). 

*  Corvo,  one  of  the  Azores,  the  northernmost  of  the  whole  group,  lying  ten 
miles  north  of  Flores. 

2  "The  fact  that  the  needle  does  not  point  at  all  places  to  the  true  north  was 
early  known,  but  the  discovery  that  it  changed  its  direction  with  a  change  of 
place  is  generally  attributed  to  Columbus,  This  is  incorrect,  for  the  needle's 
departure  from  the  geographic  meridian  (called  its  variation  or  declination)  is 
marked  down  for  different  points  of  the  sea,  on  the  atlas  of  Andrea  Bianco, 
which  was  made  in  the  year  1436;  but  what  Columbus  really  did  discover  was 
a  line  of  no  variation  2\°  east  of  the  island  of  Corvo  on  the  13th  of  September 
1492"  (A.  M.  Mayer,  "  The  Earth  a  great  Magnet,"  1872,  page  253), 

See  Thomas  Brown,  Pseudoloxia  Epidemica,  1658,  Book  II,  pap-es  68,  69. 


CAN  LONGITUDE  BE  FOUND  FROM    VARIATION?       253 

{avarokiZeiv),  till  he  comes  to  within  one  mile  of  Plymouth 
on  the  east,  where  the  variation,  reaching  maximum,  is  13 
deg.  24  min.  Then  the  anatolism  (easting)  begins  to  grow 
less  as  far  as  Helmshud,  which  place  is  not  far  from  North 
Cape  in  Finmark :  there  the  north  is  pointed  to  again.  There 
are  60  degrees  of  longitude  between  Corvo  and  Helmshud, 
but  the  variation  is  greatest  at  Plymouth,  whose  longitude 
is  30  degrees."  But  though  these  statements  are  in  part 
true,  still  along  the  entire  meridian  of  the  island  of  Corvo  the 
compass  does  by  no  means  point  due  north.  Neither  in  the 
whole  meridian  of  Plymouth  at  other  places  is  the  variation 
13  deg.  24  min.,  nor  in  other  parts  of  the  meridian  of  Helms- 
hud does  the  needle  point  to  the  true  pole.  For,  on  the 
meridian  passing  through  Plymouth  at  lat.  60  deg.,  the 
north  by  east  variation  is  greater ;  in  lat.  40  deg.  it  is  much 
less ;  in  lat.  20  deg.  it  is  very  small  indeed.  On  the  meridian 
of  Corvo,  though  the  variation  near  the  island  is  nil,  yet 
in  lat.  55  deg.  the  variation  north  by  west  is  about  \\  in  lat. 
20  deg.  the  variation  is  ;^  of  a  point  toward  the  east.  Hence 
the  bounds  of  variation  are  not  properly  defined  by  great 
meridian  circles,  and  far  less  are  the  ratios  of  increase  or 
decrease  toward  a  given  region  of  the  heavens  investigated  by 
that  method.  Therefore  the  rules  of  clattiimen  (declining)  or 
auxanomen  (increasing),  anatolism  (easting)  or  dysism  (west- 
ing), cannot  possibly  be  found  by  that  device.  The  grounds 
of  variation  in  the  southern  regions  of  the  earth,  which 
Stevinus  thereafter  searches  into  in  the  same  way,  are  utterly 
vain  and  absurd  ;  they  have  been  put  forth  by  some  Portuguese 
mariners,  but  they  do  not  agree  with  investigations:  equally 
absurd  are  sundry  observations  wrongly  accepted  as  correct. 
But  the  method  of  finding  the  port  on  long  voyages  to  distant 
parts  by  means  of   accurate   knowledge  of   the  variation  (a 


254  WILLIAM  GILBERT. 

method  invented  by  Stevinus  and  recorded  by  Grotius)  is  of 
great  importance,  if  only  fit  instruments  be  at  hand  wherewith 
the  deviation  may  positively  be  ascertained  at  sea. 


CHAPTER  X. 

WHY  IN  VARIOUS  PLACES   NEAR   THE  POLE  THE  VARIATIONS 
ARE   MUCH   AMPLER   THAN   IN   LOWER   LATITUDES. 

On  the  equator  or  near  it,  the  variation  of  a  needle  is  often 
trifling,  not  unusually  it  is  null.  In  higher  latitudes,  as  60, 
70,  80  degrees,  the  variations  are  not  infrequently  very  great. 
The  reason  of  this  is  found  partly  in  the  nature  of  the  earth, 
partly  in  the  position  of  the  versorium.  The  earth  causes 
magnetic  bodies  to  rotate  and  directs  them  poleward  strongly 
at  the  equator;  at  the  poles  there  is  no  direction,  but  only  fast 
coition  of  terminals  that  agree.  Hence  direction  is  weaker  at 
the  poles,  because  the  versorium,  by  reason  of  its  tendency  to 
turn  to  the  pole,  dips  greatly,  and  is  but  feebly  directed ;  but 
the  force  of  the  lands  and  eminences  is  strong,  with  an  energy 
proceeding  from  the  entire  earth,  and,  besides,  the  causes  of 
variation  are  nearer :  therefore  the  versorium  deflects  more  to 
those  eminences.  It  must  be  known  also  that  the  direction  of 
a  versorium  poised  on  a  needle  toward  the  plane  of  the 
horizon  is  much  stronger  at  the  equator  than  anywhere  else 
by  reason  of  the  lie  of  the  versorium  ;  and  in  proportion  as 
latitude  increases  the  direction  is  less  strong,  for  at  the 
equator  the  versorium  is  directed  naturally  toward  the  plane 
of  the  horizon,  but  in  other  places  it  is  forced  to  be  in  equiHb- 


CARDAN'S  ERROR.  2$$ 

rium  and  remains  in  equilibrium  because  of  an  external  force : 
by  its  nature  it  dips  under  the  horizon  as  the  latitude  in- 
creases, as  will  be  shown  in  the  Book  on  Inclination  or  Dip. 
Wherefore  direction  becomes  weaker  and  at  the  pole  itself  is 
null.  For  this  reason  a  weak  direction  is  easily  overcome  by 
powerful  causes  of  variation,  and  near  the  pole  the  needle 
deflects  more  from  the  meridian.  This  is  demonstrated  with 
a  terrella,  on  which  is  put  an  iron  wire  of  two  finger-breadths : 
the  wire  is  quickly  and  strongly  directed  toward  the  poles  on 
a  meridian,  but  in  the  intervals  between  equator  and  pole  it  is 
directed  weakly ;  herein  we  may  see  the  great  tendency  to 
variation  near  the  poles. 


CHAPTER  XI. 

cardan's  error  in  seeking  to  determine  the  distance 

OF  THE  earth's  CENTRE  FROM  THE  CENTRE  OF  THE 
WORLD  BY  MEANS  OF  THE  LOADSTONE  (iN  HIS  Be  Pro- 
portionibus,  V). 

How  very  easy  it  is  to  make  mistakes  and  errors  in  the 
absence  of  trustworthy  experiments,  while  investigating  the 
hidden  causes  of  things,  is  well  shown  by  a  gross  blunder  of 
Cardan,  who  thinks  he  has  discovered  the  distances  of  the 
centres  of  the  earth  and  the  world  through  the  variation  of  the 
magnetic  needle  over  nine  degrees ;  for  he  believed  that  the 
variation  point  in  the  horizon  is  everywhere  distant  eastward 
nine  degrees  from  due  north:  on  this  basis  he  establishes  a 
demonstrative  ratio  of  the  different  centres. 


256  WILLIAM  GILBERT, 


CHAPTER  XII. 

OF  FINDING  THE  AMOUNT  OF  THE  VARIATION;  WHAT  THE 
QUANTITY  IS  OF  THE  ARC  OF  THE  HORIZON  FROM  ITS 
ARCTIC  OR  ANTARCTIC  INTERSECTION  BY  A  MERIDIAN 
TO  THE  POINT  TOWARD  WHICH  THE  NEEDLE  TURNS. 

The  true  meridian  is  the  principal  basis  of  the  whole  ques- 
tion ;  when  that  is  surely  known  it  is  easy,  with  the  mariner's 
compass  (when  you  know  its  construction  and  how  the  iron 
bars  are  fixed  in  it),  or  with  any  large  horizontal  versorium,  to 
show  the  arc  of  variation  on  the  horizon.  A  variation  com- 
pass of  good  size,  after  you  have  made  two  observations  of  the 
sun  before  and  after  noon,  shows  the  variation  by  the  shadow ; 
the  sun's  altitude  is  observed  with  a  radius^  or  with  a  large 
quadrant.  On  account  of  the  greater  size  of  the  instrument, 
there  is  an  easier  and  surer  way  of  finding  the  variation  on 
shore.  Get  a  thick  plank  of  suitable  timber,  two  feet  long, 
sixteen  inches  broad  ;  on  it  describe  several  semicircles,  as  in 
the  accompanying  plate,  but  more  numerous.  In  the  centre 
erect  perpendicularly  a  brass  stilus  ;  let  there  be  also  a  rotatory 
pointer  reaching  from  the  centre  to  the  outermost  semicircle, 
and  a  magnetized  versorium  in  a  box  with  glass  cover.     Then 

^  Radius — radius  astronomicus — measuring-rod,  same  as  radiometer.  An 
old  instrument  for  measuring  angles;  the  cross-staff;  Jacob's-staff  ;  a  kind  of 
astrolabe.  (For  Radius  and  Quadrant,  etc.,  consult  R.  Ainsworth's  "  Latin 
Diet.;"  the  "Century  Diet.,"  Volumes  III,  page  3213;  V,  pp.  4883,  4934-4935  ; 
J.  E.  Worcester,  "  Diet,  of  Eng.  Lang.,"  1881,  Vol.  I,  page  786;  Vol.  II,  page 
1163;  Noah  Webster,  "Int.  Diet.,"  1891,  pp.  1171,  1399;  Dr.  John  Ogilvie, 
"  The  Imp.  Diet.,"  1882,  Vols.  I,  page  631;  II,  page  657;  III,  page  585  ;  John- 
son's "Diet,  of  Eng.  Lang.,"  London  1876,  Vol.  II,  pp.  5  and  676). 


FINDING    THE  AM.OUNT  OF   THE    VARIATION.         2$/ 


258  WILLIAM  GILBERT 

when  the  plank  is  placed  accurately  to  the  level  of  the  horizon 
by  the  plane  instrument  with  its  perpendicular  {instrumento 
piano  cum  suo  perpendiculo),  turn  the  extremity  of  the  pointer 
toward  the  north,  so  that  the  versorium  shall  rest  just  on  the 
midline  of  its  case,  which  regards  the  point  of  variation  in  the 
horizon.  Afterwards,  at  some  convenient  hour  in  the  morning 
— 8  or  9  o'clock^observe  the  point  of  the  shadow  cast  by  the 
stilus  when  it  reaches  the  nearest  semicircle,  and  mark  with 
chalk  or  ink  the  place  of  the  shadow's  point ;  now  bring  the 
pointer  round  to  that  mark  and  note  with  another  mark  the 
number  of  the  degree  in  the  horizon  shown  by  the  pointer. 
In  the  afternoon,  see  when  the  extremity  of  the  shadow  again 
reaches  the  periphery  of  the  same  semicircle,  and,  bringing  the 
pointer  around  to  the  tip  of  the  shadow,  find  the  degree  at  the 
other  side  of  the  lily.  From  the  difference  in  degrees,  you  find 
the  variation :  the  less  being  substracted  from  the  greater,  the 
half  of  the  remainder  is  the  arc  of  variation.  The  amount  of 
variation  is  sought  to  be  determined  with  many  other  instru- 
ments and  in  many  other  ways,  in  conjunction  with  the  mar- 
iner's compass — by  means  of  a  globe,  number,  and  by  the  ratio 
of  triangles  and  of  sines,  the  latitude  being  known  and  one 
observation  of  the  altitude  of  the  sun  being  made.  But  these 
methods  and  means  are  of  little  advantage,  for  it  is  useless  to 
seek  in  roundabout  ways  and  by  intricate  paths  what  you  may 
find  more  quickly  and  more  surely  by  taking  a  shorter  road. 
The  whole  trick  consists  in  proper  use  of  the  instruments  by 
which  the  sun's  position  is  ascertained  readily  and  quickly  (as 
the  sun  does  not  stand  still  but  moves  on),  for  either  the  hand 
trembles,  or  the  eyesight  is  defective,  or  the  instrument  does 
not  work  aright.  Besides,  to  observe  the  sun's  altitude  on  both 
sides  of  the  meridian,  is  as  easy  as  to  observe  it  on  one  side 
only  and  at  the  same  time  to  ascertain  the  elevation  of  the 


FINDING    THE  AMOUNT  OF   THE    VARIATION.         259 

pole.  And  he  who  can  take  one  altitude  with  an  instrument 
can  take  another,  and  if  the  one  is  doubtful,  the  whole  work 
with  globe,  number,  sines,  and  triangles  is  thrown  away.  Never- 
theless, these  exercises  of  mathematical  minds  are  praise- 
worthy. It  is  easy  for  anyone  who  stands  on  the  land,  by 
means  of  accurate  observations  and  with  the  use  of  fit  instru- 
ments, to  ascertain  the  variation,  especially  in  a  rather  right 
sphere ;  but  at  sea,  in  view  of  the  motion  and  the  turning  of 
the  waters,  experiments  cannot  be  made  with  exactness  as  to 
degrees  and  minutes,  and,  in  fact,  with  the  instruments  in  com- 
mon use,  hardly  within  one  third  or  one  half  of  a  point,  partic- 
ularly in  high  latitude :  hence  so  many  incorrect  and  faulty 
records  of  observations  by  navigators.  As  for  us,  we  have 
contrived  a  method  of  finding  the  variation,  by  means  of  a 
convenient,  handy  instrument,  from  the  rising  of  certain  stars, 
the  rising  or  setting  of  the  sun,  in  northern  regions,  from  the 
pole-star ;  for,  at  sea,  when  the  ship  is  tossed  by  the  waves, 
even  the  skilled  observer  determines  the  variation  more  surely 
with  the  aid  of  a  simple  instrument  and  one  of  no  great  preci- 
sion.    Such  an  instrument  is  constructed  as  follows : 

After  the  pattern  of  a  true  and  meridional  mariner's  com- 
pass (with  a  bare  versorium  or  with  a  versorium  fastened  to  a 
card  circle),  make  an  instrument  at  least  one  foot  in  diameter  ; 
divide  its  rim  into  four  quarters,  each  subdivided  into  90  de- 
grees. Let  the  movable  compass-box  be  balanced  below  {sub- 
tuslibratd)  with  a  heavy  weight  of  16  pounds.  On  the  edge  of 
the  suspended  box  at  beginnings  opposite  quadrants,  a  semi- 
circle rising  in  the  middle  to  a  point  (conum)  is  to  be  erected 
(the  feet  of  the  semicircle  at  both  sides  being  fastened  in  holes 
on  the  margin)  so  that  the  top  of  the  conum  shall  be  perpen- 
dicular to  the  plane  of  the  compass  ;  on  its  top  a  rule  sixteen 
digits  long  is  to  be  fastened  at  its  middle  over  the  central  axis. 


26o 


WILLIAM  GILBERT. 


FINDING   THE  AMOUNT  OF  THE    VARIATION.         26l 

as  it  were  (of  the  compass-box),  like  the  beam  of  a  balance, 
with  such  a  joint  that  it  may  move.  At  the  ends  of  the  rule 
are  small  sights  with  holes  through  which  we  may  observe  the 
sun  and  stars.  By  means  of  the  rising  or  the  setting  sun  at 
the  equinoxes,  the  variation  can  be  taken  very  well  and  very 
readily  with  this  instrument.  When  the  sun  is  in  other  parts 
of  the  zodiac,  the  variation  can  also  be  determined  when  we 
have  the  altitude  of  the  pole :  that  known,  any  one  may  find, 
with  a  globe,  or  maps,  or  with  the  instrument,  the  amplitude  (of 
the  sun  or  star)  on  the  horizon  and  the  distance  from  the  true 
east  as  well  of  the  sun  as  of  the  following  fixed  stars.  Then, 
having  counted  the  degrees  and  minutes  of  the  ortive  ampli- 
tude (time  of  rising)  from  the  true  east,  we  readily  find  the 
variation.  Observe  the  foremost  star  of  the  three  in  Orion's 
belt  when  first  it  appears  on  the  horizon  ;  direct  the  instru- 
ment toward  it,  and  observe  the  versorium,  for  as  that  star 
rises  in  the  true  east,  generally  one  degree  toward  the  south, 
we  can  see  how  far  the  versorium  diverges  from  the  meridian, 
allowance  made  for  that  one  degree.  You  may  also  observe 
the  Arctic  pole-star  when  it  is  on  the  meridian  or  at  greatest 
distance  from  the  meridian  (about  3  degrees:  according  to 
the  observations  of  Tycho  Brahe  the  pole-star  is  2  deg.  55  min. 
from  the  pole),  and  with  the  aid  of  the  instrument  you  may 
determine  the  variation  scientifically,  by  adding  or  subtract- 
ing  the   due  prostaphceresis '  of  the  star's   distance  from  the 

•  Prostaphaeresis  (Gr.  previous  subtraction),  (i)  The  reduction  to  bring 
the  apparent  place  of  a  planet  or  moving  point  to  the  mean  place.  (2)  A 
method  of  computing  by  means  of  a  table  of  natural  trigonometrical  functions 
without  multiplying.  It  was  invented  by  a  pupil  of  Tycho  Brahe,  named  Wit- 
tig,  but  was  entirely  superseded  by  logarithms  ("The  Century  Diet.,"  1890, 
Vol.  IV,  page  4790).  It  is  more  generally  called  equation  of  the  centre  (L.  N. 
Bescherelle,  "Nouv.  Diet.  Nat."  1887,  Vol.  Ill,  page  1084).  Equation  of  the 
centre  is  the  difference  between  the  place  of  a  planet  as  supposed  to  move  uni- 
formly in  a  circle,  and  its  place  as  moving  in  an  ellipse    ^Noah    Webster's 


262 


WILLIAM  GILBERT. 


meridian  (if  it  is  not  in  the  meridian).  You  will  find  when  the 
pole-star  is  in  the  meridian,  the  sun's  place  and  the  hour  of  the 
night  being  known  :  even  the  practised  observer  will  easily 
know  that  without  much  error,  by  the  visible  inclination  of  the 
asterism — as  we  do  not  care  for  a  matter  of  a  few  minutes,  as 
some  do,  who  while  striving  to  get  at  the  minutes  at  sea  often 
miss  by  a  whole  point.  The  experienced  observer  will  allow 
somewhat  for  refraction  in  noting  the  rise  of  the  sun  or  stars, 
so  that  his  calculation  may  be  more  exact. 

List  of  bright,  brilliant  stars  not  far  from  the  equator,  that 
can  be  observed  in  rising  or  in  setting  from  the  altitude  of  the  pole 
and  the  declination  of  the  stars,  the  ortive  amplitude  on  the  hori- 
zon being  ascertained  on  a  globe,  or  map,  or  the  instrument  whence 
the  variation  is  determined  by  artful  calculation. 

Right  Ascension.      Declination, 

deg.  min.  deg.  min. 

Aldebaran Eye  of  Taurus 62  55  15  53  N. 

Bellatrix Left  shoulder  of  Orion 72  24  4  5  N. 

Betelgeuze Right     "          ««      ■<          83  30  6  19  N. 

Mintaka Foremost  star  in  belt  of  Orion..  77  46  i  16  S. 

Sirius Canis  Major  97  10  15  55  S. 

Procyon Canis  Minor 109  41  5  55  N. 

Alphard Bright  star  in  Hydra 137  10  5  3  S. 

Pollux South  head  of  Gemini no  21  28  30  N. 

Castor North     "      "       "       107  4  32  10  N. 

Regulus Heart  of  Leo 146  8  13  47  N. 

Denebola Tail      "       " 171  38  16  30  N. 

Spica Spica  Virginis 195  44  8  34  S. 

Arcturus  and  Bootae 29  13  21  54  N. 

Altair Heart  of  Aquila 291  56  7  35  N. 

"  Int.  Diet."  1891,  page  504).  In  ancient  astronomy,  it  is  usually  the  difference 
between  the  true  and  mean  place  of  the  centre  of  the  epicycle  {Short,  Kepler, 
Par.  43);  but  in  the  case  of  the  moon,  generally  the  angle  at  the  centre  of  the 
epicycle  between  the  true  and  mean  apogee  {Clavius;  Ozanan),  though  some- 
times the  first  inequality  {Halma,  Almagest,  Vol.  VII).  In  modern  astronomy, 
it  is  the  excess  of  the  true  over  the  mean  anomaly  {Gatiss,  Theoria  Motus,  I.  7). 
See  the  "Century  Diet.,"  1890,  Vol.  II,  page  1982;  also,  P.  Larousse,  "Grand 
Diet.  Univ.,"  1875,  Volumes  VII,  page  771,  and  XIII,  page  288;  also  Dr.  John 
Ogilvie,  "The  Imp.  Diet.,"  1882,  Vol.  II,  page  185. 


FINDING   THE  AMOUNT  OF  THE    VARIATION.         263 

An  instrument  for  finding  the  ortive  amplitude  on  the  horizon. 
Describe  the  periphery  of  a  circle  and  divide  it  into  quarters 
by  two  diameters  intersecting  at  right  angles.  One  of  the 
diameters  indicates  the  equinoctial  circle,  the  other  the  axis  of 
the  world.  Divide  the  four  quarters  in  the  usual  way,  each 
into  90  degrees,  and  to  every  fifth  or  every  tenth  degree  from 
each  end  of  the  two  diameters  in  both  directions  assign  num- 
bers on  the  two  margins  (outside  of  this  periphery)  provided 
for  the  purpose.  Then  from  each  degree  draw  a  right  line 
parallel  to  the  equator.  Next  make  a  rule,  or  alidade,  of  the 
same  length  as  the  diameter  of  the  circle  and  divided  into  the 
same  parts  exactly  as  the  diameter  which  represents  the  axis 
of  the  world.  In  the  middle  of  this  rule  let  a  small  projecting 
piece  be  left  attached  whereby  the  middle  of  the  linea  fiduci- 
alis  ^  of  the  rule  may  be  connected  with  the  centre  of  the 
circle  ;  and  to  each  fifth  or  tenth  part  of  the  rule  give  a  num- 
ber, beginning  in  the  middle  and  numbering  right  and  left. 
The  circle  represents  the  plane  of  the  meridian  ;  its  centre  rep- 
resents the  very  point  of  rising  or  setting,  i.e.,  the  intersection 
of  horizon  and  equator.  All  these  lines  equidistant  from  the 
equator,  represent  parallels  of  the  sun  and  stars  ;  the  linea 
fiducialis  of  the  rule  or  alidade  represents  the  horizon,  and  its 
parts  degrees  of  the  horizon,  beginning  at  the  point  of  rising 
or  setting.  Therefore,  if  to  the  given  latitude  of  the  place, 
as  numbered  at  each  end  of  the  diameter  that  represents  the 

^  Linea  fidicialis — fiducial  line:  (i)  The  straight  edge  of  the  alidade  of  a 
plane  table.  (2)  The  initial  line  of  a  graduated  circle  or  vernier.  (3)  Any  line 
which  is  intended  to  be  taken  as  a  standard  straight  line.  The  term  fiducial, 
in  physics,  denotes  a  fixed  position  or  character,  and  hence  is  used  as  a  basis  of 
reference  or  comparison  ("Century  Dictionary,"  1889,  Vol.  II,  page  2202, 
and  Vol.  Ill,  page  3463.  See,  likewise,  Noah  Webster's  "  International  Dic- 
tionary," 1891,  page  556  ;  L.  N.  Bescherelle,  "  Nouv.  Diet.  Nat.,"  1887,  Vol. 
II,  page  1576;  Larousse,  "Diet.  Universel,"  1872,  Vol.  VIII,  page  336;  M. 
P.  E.  Littre's  "  Dictionnaire,"  1863,  Vol.  I,  page  1665). 


264 


WILLIAM  GILBERT. 


axis'vdf  the  world,  the  linea  fiducialis  of  the  rule  l)e  applied  ; 
and  if  the  given  declination  (less  the  complement  of  the  lati- 


lltllllllllllllllllllllllllllliUIIIII»>M"»*«*MI"*l" 


I7P6IO  ^5^  '^jo  V3|0  '  ^p 


IMfilliHIMIllllllllll!IIHmi|r|lllll'|ii{lp±^ 


tude  of  the  station)  of  sun  or  any  star  from  the  equator  be 
found  on  the  rim  of  the  instrument, — then  a  section  of  aparallel 


OBSERVATIONS  MADE  BY  SEAMEN   UNTRUSTWORTHY.  265 

drawn  from  the  point  of  this  declination  in  the  horizon,  or  in 
the  linea  fiducialis,  will  show  the  ortive  amplitude  of  the  given 
star  or  of  the  sun  at  the  stated  latitude  of  the  place. 


CHAPTER   XIII. 

OBSERVATIONS  MADE  BY  SEAMEN  COMMONLY  VARY  AND  ARE 
UNTRUSTWORTHY,  PARTLY  THROUGH  MISTAKES  AND 
WANT  OF  KNOWLEDGE  AND  THE  IMPERFECTNESS  OF  THE 
INSTRUMENTS,  AND  PARTLY  BECAUSE  THE  SEA  IS  SEL- 
DOM SO  CALM  BUT  SHADOWS  OR  LIGHTS  MAY  REST  ON 
THE  INSTRUMENTS. 

From  the  time  when  first  the  variation  of  the  needle  was 
noticed,  many  alert  navigators  have  in  sundry  ways  striven  to 
investigate  the  difference  in  the  direction  of  the  mariner's 
compass ;  but  this  has  not  been  done  with  the  exactness  that 
was  requisite,  much  to  the  disadvantage  of  the  art  of  naviga- 
tion. For,  either,  being  unlearned,  they  knew  of  no  sure 
method,  or  they  used  ill-constructed  and  unsuitable  instru- 
ments, or  they  adopted  some  conjecture  based  merely  on  the 
false  hypothesis  of  some  prime  meridian  or  magnetic  pole  ; 
while  many  copy  others'  writings  and  pass  off  for  their  own  the 
observations  of  earlier  writers  :  and  these  early  authors,  how- 
ever stupid  the  writings  in  which  they  entered  their  observa- 
tions, are  held  in  high  respect  just  because  of  their  antiquity  ; 
and  their  posterity  hold  it  to  be  not  safe  to  differ  from  them. 
Hence  on  long  voyages,  especially  to  the  East  Indies,  the  in- 
exact records  o:f  variation  of  the  compass  kept  Jby  the  Portu- 


266  WILLIAM  GILBERT. 

guese  are  prized  ;  but  whoever  reads  what  the  Portuguese  have 

written  will  quickly  see  that  in  very  many  respects  they  are 
mistaken,  and  that  they  did  not  rightly  understand  the  con- 
struction and  the  use,  in  taking  the  variation  of  the  compass  of 
Portugal  (in  which  the  lily  points  one  half  point  west  from  the 
magnetized  needle).  Hence  while  they  exhibit  the  variation 
of  the  compass  in  different  places,  it  is  not  certain  whether 
they  measure  the  deviation  with  a  true  meridional  compass  or 
with  some  other  kind,  in  which  the  magnetized  iron  points 
away  from  the  lily.  The  Portuguese  (as  is  seen  in  their  writ- 
ings) employ  the  compass  of  Portugal,  in  which  the  magnetized 
iron  is  one  half  of  a  point  to  the  east  of  the  lily. 

Even  expert  navigators  find  it  very  difficult  to  observe  the 
variation  at  sea  on  account  of  the  ship's  motions  and  her  toss- 
ing in  every  direction,  though  they  may  employ  the  best  in- 
struments yet  devised  and  in  use.  Hence  have  arisen  various 
opinions  about  magnetic  deviation.  For  example,  the  Portu- 
guese navigator  Roderigues  de  Lazos  takes  it  to  be  one  half 
point  off  the  island  of  St.  Helena ;  the  Dutch,  in  their  nauti- 
cal journal,  make  it  one  point  there ;  Kendall,  an  expert  Eng- 
lish navigator,  makes  it  only  one  sixth  of  a  point,  using  a  true 
meridional  compass.  Diego  Alfonso  finds  no  variation  at  a 
point  a  little  southeast  of  Cape  das  Agulhas,  and  by  the  astro- 
labe shows  that  the  compass  stands  in  the  true  meridian  ;  but 
Roderigues  declares  that  the  compass  points  due  north  and 
south  at  Cape  das  Agulhas  if  it  be  of  the  Portuguese  style,  in 
which  the  variation  is  one  half  point  to  the  southeast.*     There 

1  Cape  Agulhas — Cape  Aguilhas — Capo  d'Aguhas — southernmost  point  of 
Africa.  This  name  was  given  by  the  Portuguese  on  account  of  the  magnetic 
derangement  of  their  compass  needles  in  its  locality  when  Vasco  de  Gama 
sailed  round  it — Aguilhas,  in  Portuguese,  signifying  needles.  (Walker,  "  Magn. 
of  Ships,"  1853,  page  2.) 

"  And  so  likewise,  because  the  Cape  de  las  AguUas  hath  sea  on  both  sides 


VARIATION  OF   THE  MAGNETIZED   NEEDLE.  267 

is  the  same  degree  of  confusion,  carelessness,  and  falsity  in 
most  of  the  other  records. 


CHAPTER  XIV. 

OF    THE    VARIATION    UNDER    THE    EQUINOCTIAL    LINE    AND 

NEAR   BY. 

In  northern  regions  the  compass  varies  because  of  the 
northern  eminences ;  in  southern  regions  because  of  the  south- 
ern eminences ;  on  the  equator,  if  the  eminences  on  both  sides 
were  equal,  there  would  be  no  variation.  But  because  this  sel- 
dom happens,  therefore  oftimes  variation  is  observed  under 
the  equator  ;  and  even  at  some  distance  from  the  equator, 
three  or  four  degrees,  variation  may  be  produced  by  austral 
eminences,  if  extensive  and  potent  austral  continents  lie  near 
on  one  side. 


CHAPTER  XV. 

THE  VARIATION  OF  THE  MAGNETIZED  NEEDLE  IN  THE  GREAT 
SEA,   ETHIOPIC   AND  AMERICAN,  BELOW   THE  EQUATOR. 

We  have  already  spoken  of  the  mode  and  reason  of  varia- 
tion in  the  great  Atlantic  Sea ;  but  below  the  equator,  on  the 

near  it,  and  other  land  remote,  and  as  it  were  aequidistant  from  it,  therefore  at 
that  point  the  needle  conforms  unto  the  true  meridian,  and  is  not  distracted  by 
the  vicinity  of  Adjacencies.  This  is  the  general  and  great  cause  of  variation  " 
(Sir  Thomas  Brown,  Pseudoloxia  Epidemica,  1658,  Book  H,  page  70).  See  the 
extract  from  unpublished  letter  of  Mr.  Archibald  Smith  to  Lord  Cardwell,  dated 
February  13,  1866,  relative  to  the  loss  of  the  iron  steamer  "  Eastern  Province" 
near  Cape  Agulhas,  at  page  387  of  "  Good  Words  "  for  1879. 


268  WILLIAM  GILBERT. 

east  xoast  of  Brazil,  the  needle  swerves  toward  the  continent  j 
with  the  end  that  looks  south :  thus,  at  that  end,  it  declines 
from  the  true  meridian,  toward  the  west ;  this  is  noticed  by- 
navigators  as  a  movement  of  the  point  of  the  needle,  and  so 
they  think  that  the  variation  is  to  the  east.  But,  over  the  whole 
route  from  the  first  eastern  promontory  of  Brazil,  past  Cape 
Sao  Agostino  to  Cape  Frio  and  as  far  as  the  mouth  of  the 
Strait  of  Magelhan,  the  variation  is  always  from  south  to  west, 
the  crotch  of  the  needle  tending  to  the  Antartic  pole.  For  it 
always  turns  with  the  proper  end  toward  a  continent.  Yet  the 
variation  takes  place  not  only  on  the  coast  itself,  but  at  some 
distance  from  the  land — over  a  space  of  50  or  60  German  miles 
or  more. 

But  at  a  great  distance  from  the  land  the  arc  begins  to 
grow  less,  for  the  needle  turns  less  toward  distant  promi- 
nences ;  and  it  is  not  made  to  diverge  much  by  such  promi- 
nences when  present  and  on  the  spot,  for  it  then  shares  with 
them.  On  the  island  of  St.  Helena  (whose  longitude  is  less 
than  it  is  usually  given  in  maps)  the  compass  varies  one  or 
perhaps  two  degrees.  The  Portuguese,  and  others  who  have 
learnt  of  them,  in  sailing  beyond  the  Cape  of  Good  Hope  to 
the  Indies,  in  order  to  have  favorable  winds,  shape  their  course 
toward  the  islands  of  Tristan  de  Acunha,  and  on  the  first  half 
of  the  voyage  find  no  considerable  difference  of  variation ;  but 
near  those  islands  the  difference  is  greater  than  anywhere  else 
in  the  entire  voyage.  For  the  great  promontory  of  the 
southerly  continent  which  lies  to  the  southwest  pulls  and 
solicits  that  end  of  the  versorium  which  points  south  (and  at 
that  end  is  the  principal  cause  of  the  variation).  But  as  the 
ship  approaches  the  Cape  of  Good  Hope  the  variation  grows 
steadily  less.  In  the  prime  meridian,  at  latitude  45  degrees, 
the  needle  points  southeast  by  south  ;  and  so,  too,  he  who 


VARIATION  IN  NOVA    ZBMBLA.  269 

sails  along  the  coast  from  Manicongo  to  the  tropic  and  a  little 
beyond  will  find  the  needle  tending  from  the  south  to  the 
southeast,  but  not  much.  At  Cape  das  Agulhas  it  still  keeps 
a  little  of  the  variation  it  showed  near  the  islands  of  Tristan 
de  Acunha,  but  it  is  much  diminished  owing  to  the  remoteness 
from  the  cause  of  the  variation  ;  and  the  south  end  of  the 
needle  does  not  yet  point  due  south. 


CHAPTER  XVI. 

OF  THE  VARIATION  IN  NOVA  ZEMBLA. 

The  variations  are  greatest  in  regions  nigh  to  the  poles,  as 
has  been  proved,  and  there,  too,  the  changes  of  variation  are 
sudden,  as  Dutch  observers  noted  some  years  ago,  though 
their  observations  were  not  exact ;  yet  the  inexactitude  can 
be  excused,  for,  with  the  ordinary  instruments,  it  is  hard  to 
get  at  the  truth  in  such  high  latitudes — about  80  degrees. 
But  now  the  variation  of  the  com.pass  gives  the  clear  evidence 
of  the  existence  of  an  open  passage  eastward  through  the 
North  Sea — Arctic  Ocean  {Mare  Scythicum),  for,  since  the 
compass  has  so  great  an  arc  of  variation  to  the  west,  it  is  evi- 
dent that  no  continent  stretches  for  any  great  distance  along 
that  whole  route  eastward.  Therefore  we  can  strive  and  ex- 
plore more  hopefully  for  a  passage  to  the  Moluccas  by  the 
northeast  than  by  the  northwest. 


2/0  WILLIAM  GILBERT. 


CHAPTER  XVII. 

VARIATION  IN  THE  SOUTH   SEA. 

After  passing  through  the  Strait  of  Magellan,  the  varia- 
tion off  the  Peruvian  coast  is  to  the  southeast ;  and  a  like 
deflection  continues  all  along  the  coast  of  Peru  to  the  equator. 
In  higher  latitude,  up  to  45  degrees,  the  variation  is  greater 
than  near  the  equator ;  and,  just  as  on  the  eastern  coast  of 
South  America,  the  deflection  was  from  south  toward  west, 
so  now  it  is  to  the  southeast.  From  the  equator  northward 
the  variation  is  very  small  or  null  till  you  reach  New  Galicia  ; 
thence  along  the  whole  coast  as  far  as  Quivira  the  inclination 
is  from  the  north  to  the  east. 


CHAPTER  XVIII. 

OF  THE  VARIATION  IN  THE  MEDITERRANEAN   SEA. 

Sicilian  and  Italian  mariners  declare  that  in  the  Sicilian 
sea  and  eastward  to  the  meridian  of  Peloponnesus  (as  Francis 
Maurolycus  relates)  the  needle  grecizes,  i.e.,  is  diverted  from 
the  pole  toward  the  wind  called  Grsecus  (Greek),  or  north 
wind ;  that  on  the  coast  of  Peloponnesus  it  points  to  the  true 
pole ;  but  that  when  you  proceed  farther,  then  it  mistralizes, 
inclining  from  the  pole  to  the  mistral  or  northwest  wind :  this 
is  in  accordance  with  our  rule   of  the  variation.     For,  as  the 


VARIATION  IN  INTERIOR   OF  CONTINENTS.  2^1 

Mediterranean  Sea  stretches  away  from  that  meridian  toward 
the  west,  so,  on  the  side  toward  the  east,  there  is  open  sea  as 
far  as  Palestine,  and  toward  the  north  and  east  is  the  whole 
archipelago,  and  hard  by  the  Black  Sea.  From  Peloponnesus 
to  the  north  pole,  that  meridian  passes  through  the  largest 
and  most  elevated  regions  of  all  Europe  :  through  Achaia, 
Macedonia,  Hungary,  Transylvania,  Lithuania,  Livonia,  Novo- 
goroda,  Corelia  and  Biarmia/ 


CHAPTER  XIX. 

THE  VARIATION  IN    THE    INTERIOR    OF  THE    GREAT    CONTI- 
NENTS. 

Great  seas  usually  have  great  variations ;  in  some  parts, 
however,  there  is  no  variation,  but  true  direction  poleward. 
On  the  continents,  too,  the  needle  often  deflects  from  the 
meridian,  as  on  the  margin  of  the  land  and  the  confines,  but 
the  arc  of  variation  is  wont  to  be  small :  in  the  middle  regions 
of  great  continents  there  is  no  variation.  Hence  in  the  heart 
of  northern  Europe  and  of  Asia,  in  the  interior  of  Africa,  Peru, 
and  of  North  or  Mexican  America,  the  versorium  rests  in  the 
meridian. 

*  Biarmia  is  the  name  given  by  Scandinavian  writers  to  that  section  of  N.  E. 
Russia  bordering  upon  the  White  Sea.  See  reference  thereto  in  note,  Book  I, 
Chap.  I,  of  present  work. 


272:  WILLIAM  GILBERT. 


CHAPTER  XX. 

THE  VARIATION  IN  THE  EASTERN  OCEAN. 

The  variation  in  the  Eastern  Ocean,  all  the  way  to  Goa 
and  the  Moluccas,  is  noted  by  the  Portuguese,  but  they  are 
mistaken  in  very  many  points,  for  they  follow  the  first  observ- 
ers who  set  down  the  variations  for  sundry  places,  ascertained 
by  the  use  of  unfit  instruments,  or  by  inaccurate  observations, 
or  by  conjecture.  Thus  in  the  island  of  Brando'  they  make 
the  compass  vary  22  degrees  to  the  northwest.  Now,  in  no 
region,  in  no  place  on  earth  that  has  not  a  higher  latitude 
than  that,  is  the  variation  so  much  as  22  degrees  :  in  fact  the 
deviation  on  that  island  is  trifling.  So,  when  they  say  that  in 
Mozambique  the  compass  varies  to  the  northwest  one  point, 
they  are  in  error  even  though  the  compass  they  use  is  that  of 
Portugal ;  for,  without  a  doubt,  the  needle  varies  in  Mozam- 
bique to  the  southwest  one  quarter  of  a  point  or  more. 
Again,  they  are  all  wrong  in  holding  that  beyond  the  equator, 
on  the  route  toward  Goa,  the  compass  varies  westward  one 
point  and  one  half ;  better  had  they  said  that  in  the  first  part 
of  the  route  the  compass  of  Portugal  inclines  one  point,  but 
that  a  true  or  meridional  compass  varies  only  one-half  point. 
Yet  to  determine  the  amount  of  the  variation  in  the  Eastern 
Ocean  according  to  our  rules,  we  need  a  more  exact  and  cor- 
rect reconnoissance  of  the  austral  continent,  which  stretches 
farther  from  the  south  toward  the  equinoctial  than  it  is  de- 
scribed in  current  charts  and  globes. 

'  The  island  of  Brando  lies  in  the  Gulf  of  Bothnia,  close  by  the  east 
coast  of  Sweden. 


DEVIATION   VARIES  ACCORDING    TO  DISTANCE.      273 


CHAPTER  XXI. 

HOW  THE  DEVIATION   OF   THE   NEEDLE   IS  GREATER  OR   LESS 
ACCORDING  TO   THE   DISTANCES   OF   PLACES. 

In  the  heart  of  great  continents  there  is  no  variation ;  so, 
too,  in  the  midst  of  great  seas.  On  the  edge  of  such  lands  and 
seas  the  variation  is  often  large,  but  not  as  great  as  it  is  a  little 
out  at  sea :  thus  off  Cape  Sao  Agostino  there  is  variation,  but 
50  miles  away  to  the  east  there  is  a  larger  variation  ;  still  larger 
80  miles  away  and  100  miles  away.  But  from  100  miles  dis- 
tance the  reduction  of  the  deviation  is  slower  as  you  approach 
the  continent  than  from  the  distance  of  80  miles,  and  from  80 
miles  than  from  50;  for  the  deviation  is  changed  and  reduced 
somewhat  more  quickly  as  you  come  toward  the  shore  from 
anear  then  from  afar.  So,  for  mariners  approaching  New- 
foundland, the  change  of  the  variation  is  quicker  (i.e.,  a  degree 
of  variation  is  lost  in  a  less  arc  of  the  route  on  a  parallel)  when 
they  are  not  far  from  land  than  when  they  are  100  miles  away  ; 
but  when  they  journey  inland  the  changes  are  more  tardy  at 
firi;t  than  when  they  come  farther  into  the  interior. 

The  figure  shows  the  ratio  of  the  arcs  on  a  parallel  circle 
while  a  versorium  is  brought  toward  a  continent  that  reaches 
to  the  pole ;  the  ratio  answers  to  the  degrees  of  the  variation. 
Let  A  be  the  pole,  B  the  elevation  of  a  great  mass  of  land. 
At  C  there  is  no  variation  caused  by  B,  which  is  too  distant ; 
at  D  the  variation  is  greatest,  because  there  the  needle  is  at- 
tracted or  is  made  by  the  whole  earth  to  turn  to  the  projecting 
land  B  ;  nor  is  the  needle  hindered,  nor  checked,  nor  led  tow?'-d 


274  WILLIAM  GILBERT. 

the  pole  by  the  verticity  of  this  land,  but,  tending  to  the  pole, 
it  is  nevertheless  deflected  therefrom,  because  of  the  site  or 
position  and  convenient  distance  of  the  overmastering  eleva- 
tions of  land. 


But,  now,  from  C  to  D  the  variation  grows,  yet  the 
versorium  does  not  deviate  so  quickly  in  the  first  stages  as 
it  does  when  near  D.  But  you  sail  more  miles  on  the  parallel 
circle  CD  as  long  as  you  are  near  C,  to  register  one  degree  of 
variation,  than  you  sail  when  near  D ;  so,  too,  in  travelling  from 
D  toward  E  you  must  make  a  greater  number  of  miles  when 
near  D  than  when  near  E.  Thus  there  are  equal  deviations 
for  unequal  distances  sailed,  both  for  rising  and  falling  varia- 
tion ;  yet  it  falls  within  a  less  space  than  it  rises.  There  are, 
however,  several  other  incidental  cases  that  confuse  this  ratio. 


BOOK  V. 
CHAPTER  I. 

OF  THE  DIP  OF  THE   MAGNETIC  NEEDLE. 

We  come  at  last  to  that  fine  experiment,  that  wonderful 
movement  of  magnetic  bodies  as  they  dip  beneath  the  horizon 
in  virtue  of  their  natural  verticity  ;  after  we  have  mastered  this, 
the  wondrous  combination,  harmony,  and  concordant  interac- 
tion of  the  earth  and  the  loadstone  (or  magnetized  iron),  being 
made  manifest  by  our  theory,  stand  revealed.  This  motion  we 
have  so  illustrated  and  demonstrated  with  many  experiments, 
and  purpose  in  what  follows  so  to  point  out  the  causes  and 
reasons,  that  no  one  endowed  with  reason  and  intelligence  may 
j  ustly  contemn,  or  refute,  or  dispute  our  chief  magnetic  principles. 
Direction,  as  also  variation,  is  demonstrated  on  the  plane  of  the 
horizon  whenever  a  magnetic  needle  poised  in  equilibrium 
comes  to  a  rest  in  any  fixed  point  of  it.  But  inclination  (dip) 
is  seen  to  be  the  motion  of  the  iron  bar,  first  balanced  on  its 

axis  and  then  excited  by  a  loadstone,  from  that  point  in  the 

275 


276  WILLIAM  GILBERT. 

horizon,  one  end  or  pole  tending  toward  the  earth's  centre. 
And  we  have  found  that  this  inclination  differs  in  the  ratio  of 
the  latitude  of  each  region.  Now  this  movement  is  produced 
not  by  any  motion  away  from  the  horizon  toward  the  earth's 
centre,  but  by  the  turning  of  the  whole  of  the  magnetic  body  to 
the  whole  of  the  earth,  as  later  we  will  show.  Nor  does  the 
needle  descend  below  the  horizon  in  the  ratio  of  the  degrees  of 
the  elevation  of  the  pole  in  the  given  region,  and  with  an  equal 
arc  of  the  quadrant  in  any  oblique  sphere,  as  later  will  be  seen. 
But  how  much  the  needle  dips  in  every  horizon  can  now  first 
be  ascertained  by  means  of  an  instrument  (which,  however,  is 
not  very  easily  constructed),  just  as  in  sun-dials  when  the  needle 
returns  to  points  in  the  horizon,  or  as  in  the  mariner's  compass. 
Get  a  circular  planed  board  with  diameter  at  least  six  finger- 
lengths,  which  is  to  be  fastened  to  one  face  of  an  upright  square 
post  and  to  rest  on  a  wooden  base.  Divide  the  periphery  of 
the  instrument  into  four  quadrants,  and  then  each  quadrant 
into  ninety  degrees.  In  the  centre  of  the  instrument  drive  a 
brass  nail,  and  in  the  centre  of  its  head  bore  a  small  hole  well 
reamed  and  smoothed.  Adjust  to  the  instrument  a  circle  or 
ring  of  brass  about  two  finger-breadths  wide,  with  a  transverse 
plate  or  fiat  bar  of  the  same  metal  fastened  across  the  middle 
of  the  ring  and  serving  for  horizon.  In  the  middle  of  this 
horizon  bar  bore  another  hole  which  shall  be  exactly  opposite 
to  the  centre  of  the  instrument,  in  which  a  hole  was  already 
bored.  Next  get  a  steel  wire  such  as  is  used  for  compass 
needles,  and  at  the  exact  middle  of  it  and  at  right  angles  to  it 
pass  a  very  thin  iron  axis  through  it  so  that  the  middle  of  the 
axis  and  the  middle  of  the  needle  shall  exactly  meet ;  let  this 
inclination  (dipping)  needle,  the  ends  of  the  axis  having  been 
inserted  into  the  holes,  be  suspended  so  that  it  may  move  freely 
and  evenly  on  itself  in  most  exact  equilibrium,  and  so  accu- 


DIP   OF   THE  MAGNETIC  NEEDLE.  7.TI 


Dip  Instrument. 


2/8  WILLIAM  GILBERT 

rately  that  it  may  not  turn  away  from  any  one  degree  or  point 
marked  on  the  circumference  more  than  from  any  other,  but 
may  rest  easily  at  any  one  point.  Have  the  instrument  fastened 
upright  to  the  face  of  the  post,  and  on  the  edge  of  the  base 
set  a  very  small  magnetized  versorium.  The  needle  thus 
nicely  balanced,  now  rub  skilfully  at  both  ends  with  the  oppo- 
site poles  of  a  loadstone,  but  do  this  with  the  greatest  care  lest 
the  wire  be  in  the  least  bent ;  for  unless  you  do  all  this  with 
great  skill  and  dexterity,  you  will  reach  no  result.  Next  get  a 
second  brass  ring,  a  little  larger  than  the  first,  so  as  to  go  round 
it,  and  to  one  rim  fit  a  cover  of  glass  or  of  very  thin  mica ;  this, 
when  placed  over  the  other  ring,  encloses  the  whole  space,  and 
the  needle  is  protected  from  dust  and  currents  of  air.  The  in- 
strument being  now  complete,  set  it  up  perpendicularly  with 
the  small  versorium  on  the  base,  so  that  when  thus  erected 
exactly  upright  it  may  tend  to  the  true  point  of  the  magnetic 
direction.  Then  that  one  of  the  needle's  ends  which  in  north- 
ern latitudes  looks  to  the  north  dips  below  the  horizon  ;  but  in 
southern  latitudes  the  end  of  the  needle  that  looks  south  tends 
toward  the  earth's  centre  in  a  certain  ratio  (afterward  to  be  ex- 
plained) of  the  latitude  of  the  region  in  question  from  the 
equator  on  either  side.  But  the  needle  must  be  rubbed  with  a 
powerful  loadstone,  else  it  does  not  dip  at  the  true  point  or 
goes  beyond  it  and  is  not  always  at  rest  in  it.  A  larger  instru- 
ment can  also  be  employed,  of  ten  or  twelve  finger-lengths  diam- 
eter, but  in  that  case  there  is  more  trouble  in  balancing  the 
needle  exactly.  Care  must  be  taken  to  have  the  needle  of 
steel,  also  that  it  be  straight,  and  that  the  sharp  points  of  the 
axis  on  both  ends  be  at  right  angles  with  the  needle  itself,  and 
that  it  pass  through  the  very  centre. 

As  in  other  magnetic  movements  there  is  strict  agreement 
and  a  clearly  visible,  sensible  accordance  between  the  earth  and 


DIP    OF   THE  MAGNETIC  NEEDLE.  2/9 

the  loadstone  in  our  demonstration,  so  in  this  inclination  is 
the  accordance  of  the  globe  of  the  earth  and  the  loadstone 
positive  and  manifest.  The  true  and  definite  cause  of  this 
great  and  hitherto  unknown  effect  is  as  follows:  The  loadstone 
moves  and  revolves  until  one  of  its  poles,  being  impelled  toward 
the  north,  comes  to  rest  in  its  predetermined  point  on  the 
horizon ;  the  pole  that  comes  to  a  stand  looking  north  is  (as 
appears  from  the  foregoing  rules  and  demonstrations)  southern, 
not  northern,  though  till  now  every  one  has  supposed  it  to  be 
northern  because  it  turns  to  the  north.  An  iron  wire  or  ver- 
sorium  touched  with  this  pole  of  the  stone  turns  south,  and  is 
made  northern  because  rubbed  at  the  south  end  of  the  stone; 
just  as  when  the  point  of  a  versorium  is  magnetized  in  that  way- 
it  will  be  directed  toward  the  earth's  south  pole  and  to  that 
will  turn,  while  the  other  end,  the  crotch,  will  be  southern  and 
will  turn  to  the  northern  regions  of  the  earth  (the  earth  itself 
causing  the  motion),  for  thus  does  direction  result  from  the 
bearings  of  the  stone  and  the  needle,  and  from  the  earth's  ver- 
ticity.  But  inclination  (dip)  is  when  the  needle  turns  to  the 
body  of  the  earth,  its  south  end  pointed  to  the  north,  in  any 
latitude  away  from  the  equator.  For  it  is  a  fixed  and  unchang- 
ing law  that  exactly  beneath  the  celestial  equator,  or  rather  on 
the  equator  of  the  terrestrial  globe,  the  magnetic  incHnation  or 
dip  of  the  needle  is  nil;  and  in  whatever  way  it  may  have  been 
excited  or  rubbed,  it  rests  exactly  on  the  plane  of  the  horizon 
in  the  inclination  instrument,  provided  it  be  first  duly  balanced. 
The  reason  of  this  is,  that  the  needle,  being  at  equal  distance 
from  the  two  poles,  does  not  in  its  rotation  dip  toward  either, 
but  stands  balanced,  pointing  to  the  level  of  the  equator,  as  it 
does  when  mounted  on  a  sharp  point  or  floating  free  and  un- 
hindered on  water. 

But  when  the  needle  is  in  any  latitude  from  the  equator,  or 


280  WILLIAM  GILBERT. 

when  one  of  the  earth's  poles  is  raised  (I  do  not  say  raised 
above  the  visible  horizon,  like  what  is  commonly  reputed  to  be 
the  pole  of  the  revolving  world  in  the  heavens,  but  raised 
above  the  horizon  of  the  centre  or  above  its  own  diameter, 
equidistant  from  the  plane  of  the  visible  horizon,  which  is  the 
true  elevation  of  the  earth's  pole),  then  inclination  appears  and 
the  needle  dips  in  its  meridian  towards  the  body  of  the  earth. 
Thus,  let  AB  be  the  visible  horizon  of  a  region;  CD  the 
earth's  horizon,  dividing  the  earth  into  equal  parts  ;  EF  the 
earth's  axis  ;  G  a  place  within  the  region  :  plainly  the  north  pole 
E  rises  above  the  point  C  by  as  much  as  G  is  distant  from  the 
equator  ;  therefore,  since  at  E  the  magnetized  needle  is  raised 


to  perpendicular  just  by  its  turning  (to  the  north),  as  has  already 
been  shown,  so  now  at  G  there  is  a  sort  of  beginning  of  such 
a  turning,  proportioned  to  the  latitude  (the  magnetized  body 
departing  from  the  plane  of  the  horizon),  and  the  needle  inter- 
sects at  unequal  angles  the  horizon  and  shows  dip  beneath  the 
horizon ;  for  this  reason,  if  the  dipping  needle  be  placed  at  G, 
its  south  end  (that  which  points  north)  descends  below  the 
plane  of  the  visible  horizon  AB.  Thus  there  is  very  great  dif- 
ference between  a  right  and  a  polar  or  parallel  sphere,  in  which 


DIP   OF   THE  MAGNETIC  NEEDLE. 


281 


the  pole  is  in  the  true  zenith.  For  in  a  right  sphere  the  needle 
is  parallel  to  the  plane  of  the  horizon.  But  when  the  celestial 
pole  is  in  the  vertical  point,  or  when  the  earth's  pole  is  itself 
the  place  in  question  {Jocus  regionis),  then  the  needle  is  perpen- 
dicular to  the  horizon.  This  is  shown  on  a  terrella  ;  suspend 
in  air,  like  the  beam  of  a  balance,  a  small  dip  needle  of  only 
two  fingers-width  {duorum  digitorum)  rubbed  at  a  loadstone,  and 
carefully  bring  the  terrella  under  it,  and  first  let  the  terrella 
stand  properly  (recta)  as  in  a  right  sphere,  and,  as  in  the  first  of 
the  figures  following,  the  needle  will  now  remain  in  equilibrium. 
But  in  an  oblique  position  of  the  terrella,  as  in  an  oblique 
sphere  and  in  the  second  figure,  the  needle  dips  at  one  end 
obliquely  toward  the  neighboring  pole,  but  does  not  rest'  on 
the  pole,  nor  is  its  dip  governed  by  the  pole,  but  by  the  whole 
body  and  mass  ;  for  the  dipping  needle  in  a  higher  latitude  sinks 
— passes  {labitur) — beyond  the  pole.  But  in  the  third  position* 
of  the  terrella  the  needle  is  perpendicular,  because  the  pole  of 


the  stone  is  uppermost,  and  the  needle  tending  straight  toward 
the  body  attains  the  pole.  The  crotch  in  the  foregoing  figures 
always  turns  toward  the  north  pole  of  the  terrella,  having  been 
touched  with  its  north  pole ;  the  point   having  been  touched 


282 


WILLIAM  GILBERT. 


by  the  south  pole  of  the  terrella  tends  toward  its  south  pole. 
Thus  may  we  see  the  level,  the  oblique,  and  the  perpendicu- 
lar position  of  the  needle  on  a  terrella.* 


CHAPTER  II. 

DIAGRAM  SHOWING  DIP  OF  THE  MAGNETIC  NEEDLE  IN  DIF- 
FERENT POSITIONS  OF  A  SPHERE  AND  HORIZONS  OF  THE 
EARTH  IN  WHICH  THERE  IS  NO  VARIATION  OF  DIP. 


Let  AB  be  the  equator,  C  the  Arctic  and  D  the  Antarctic 
pole,  E^  G  dipping  needles  in  northern  regions,  and  //",  F  in 


southern  regions  of  the  earth  or  the  terrella.     All  the  needles 
have  been  touched  with  the  true  Arctic  pole  of  the  terrella. 

^  At  two  points  of  the  earth's  globe,  the  needle  will  rest  in  a  vertical 
position.  These  are  the  magnetic  poles  of  the  earth.  The  northern  mag- 
netical  pole  was  discovered  June  i,  1831,  by  Sir  James  Clark  Ross,  during  the 
second  voyage  he  made  to  the  Arctic  Regions  under  his  uncle  Sir  John  Ross, 


DIAGRAM  SHOWING  DIP   OF  MAGNETIC  NEEDLE.     283 

The  figure  shows  the  needles  in  horizontal  position  at  A  and 
B,  the  earth's  and  the  terrella's  equator  ;  they  are  perpendicular 
at  the  poles  C  and  D ;  but  in  the  mid  spaces,  at  distances  of  45 
degrees,  the  crotches  dip  toward  the  south,  but  the  points 
look  toward  the  north  at  the  same  angle. 

Diagram  showing  the  direction  and  dip  of  a  terrella  represent-  * 
ing  the  earth  relative  to  the  standard  representation  of  the  globe 
of  the  earth,  at  north  latitude  50  degrees. 

A  is  the  north  pole  of  the  earth  or  of  the  large  terrella  ;  B 
its  south  pole,  C  is  the  smaller  terrella,  and  E  the  south  pole  of 
the  smaller  terrella  that  dips  toward  the  north  region  (of  the 
larger).  Its  centre  C  is  placed  on  the  superficies  of  the  larger 
terrella,  because  the  smaller  terrella  varies  a  little  on  account 
of  the  length  of  the  axis  {quia  terrella  minor  aliguantulum  vari- 
at  propter  axis  longitudineni),  but  in  the  earth  the  variation  is 
very  little.  As  the  needle  dips  in  the  latitude  of  a  region  of 
50  degrees,  so,  too,  the  axis  of  the  stone — which  is  spherical — 
is  depressed  beneath  the  horizon,  and  its  south  pole,  which  is 
within   the    circumference  of    the   larger  terrella  dips,  while 


and  lies  near  Boothia  Felix  Land  in  70°  5'  17"  N.  lat.  and  96°  46'  45"  W. 
long.,  the  dip  being  89°  59',  or  "  within  one  minute  of  the  vertical."  He  was 
not  successful,  however,  in  reaching  the  southern  magnetic  pole,  but  he 
assigned  to  it  a  position  in  75°  5'  S.  lat.  and  154°  8'  E.  long.  The  north 
magnetic  pole  is  the  point  of  the  earth's  surface  where  the  dipping-needle  rests 
with  its  magnetic  axis  vertical  and  its  true  south  pole  downwards  ;  the  south 
magnetical  pole  is  the  point  where  the  dipping-needle  rests  with  its  axis  ver- 
tical and  its  true  north  pole  downwards.  As  the  magnetism  of  the  north  mag- 
netic pole  corresponds  to  that  of  the  south  pole  of  the  magnet.  Prof.  Silvanus  P. 
Thompson  named  the  latter  "the  north-seeking  pole."  By  Prof,  Faraday  the 
north-seeking  end  was  designated  as  the  "  marked  "  and  the  other  end  the 
"unmarked,"  the  French  calling  them  the  "astral"  and  the  "boreal,"  while 
others  allude  to  them  as  the  "negative"  and  "positive"  ends,  respectively. 
(See  Capt.  Sir  John  Ross'  "  Narrative  of  a  Second  Voyage.  .  .  .,"  published  in 
1835;  Humboldt,  "Cosmos,"  article  on  Magnetic  Inclination;  Sir  Wm.  Thom- 
son's "Terrestrial  Magn.  and  the  Magn.  Compass  ;"  "  The  Earth  a  Magnet," 
in  "Cornhill  Mag.,"  Vol.  XVII,  page  727.) 


284  WILLIAM  GILBERT. 

in  the  south  (of  the  larger  terrella)  its  (the  smaller  terrella's) 
north  pole  is  raised  toward  the  zenith.  And  a  flat  circular 
piece  of  iron  carefully  magnetized  at  opposite  points  of   its 


circumference  acts  in  the  same  way ;  but  these  magnetic  ex- 
periments are  less  striking  because  in  iron  disks  the  magnetic 
force  is  rather  sluggish.  The  figure  below  shows,  with  bits  of 
iron,  the  differences  in  dip  at  various  latitudes  in  the  terrella.' 

Below  is  shown  the  dip  of  the  needle  on  a  terrella  by 
means  of  a  number  of  bits  of  iron  wire  of  equal  size,  one  bar- 
ley-corn in  length,  and  placed  in  a  meridian.  At  the  equator 
the  bits  of  iron  are  directed  toward  the  poles,  and  lie  upon  the 


1  Consult  Airy's  "  Magnetism,"  more  particularly  for  figures  and  explana- 
tions of  the  magnetic  dip  and  the  variations  of  total  terrestrial  magnetic  in- 
tensity. 


INSTRUMENT  FOR   SHOWING  DEGREE   OF  DIP.        285 

body  of  the  terrella  in  the  plane  of  its  horizon.     The  nearer 
they  are  placed  to  the  poles  the  more  do  they  rise  from  the 


horizontal  by  reason  of  their  turning  poleward  ;  at  the  poles 
they  tend  straight  to  the  centre.  But  bits  of  iron  will  not 
stand  up  aright,  save  on  a  good  loadstone,  if  they  be  too  long. 


CHAPTER  III. 

AN  INSTRUMENT  FOR  SHOWING  BY  THE  ACTION  OF  A  LOAD-  * 
STONE   THE   DEGREE    OF    DIP    BELOW  THE    HORIZON    IN 
ANY   LATITUDE. 

Description  of  the  instrument ;  its  uses. 

Make  a  perfectly  round  terrella  of  a  superior  strong  load- 
stone, one  homogeneous  throughout,  not  injured  anywhere  by 


286 


WILLIAM  GILBERT. 


INSTRUMENT  FOR   SHOWING  DEGREE   OF  DIP.        28/ 

decay  or  corrosion,  of  proper  size,  so  that  its  diameter  shall  be 
six  or  seven  finger-breadths.  Having,  by  the  method  hereto- 
fore given,  found  the  poles,  mark  them  with  some  iron  instru- 
ment, also  mark  the  equinoctial  circle.  Next,  in  a  squared 
block  of  wood,  one  foot  in  diameter,  make  a  hemispherical 
cavity  to  hold  half  of  the  terrella,  so  that  just  one  half  of  the 
terrella  shall  rise  above  the  block.  Where  the  limb  of  the 
terrella  is  nearest  the  rim  of  this  cavity  draw  a  circle  around  it 
for  a  meridian,  and  then  divide  it  into  four  equal  parts  or 
quadrants,  and  the  quadrants  each  into  90  degrees.  Let  one 
end  of  the  quadrants  on  the  limb  be  near  the  centre  of  a  quad- 
rant on  the  block,  and  divide  this  also  into  90  degrees.  At 
that  centre,  place  a  small  short  versorium  having  one  of  its 
ends  sharp  and  longer  than  the  other,  for  use  as  a  pointer,  and 
let  it  be  poised  on  a  fitting  sharp  fulcrum.  Evidently,  when- 
ever the  poles  of  the  terrella  are  at  the  beginnings  (zero)  of 
the  quadrants,  then  the  versorium  will  lie  in  a  right  line  on  the 
terrella  as  in  equilibrium.  But,  if  the  terrella  be  moved  so 
that  one  of  the  poles  rises  on  the  left,  then  the  needle  elevates 
itself  in  the  meridian  according  to  the  latitude,  just  as  a  piece 
of  magnetized  iron  rises ;  and  the  needle  indicates  upon  the 
quadrant  described  on  the  block  the  degrees  of  the  dip.  The 
rim  of  the  cavity  in  the  block  represents  a  meridian  circle,  and 
to  it  answers  some  meridian  circle  of  the  terella,  for  the  poles 
on  both  sides  are  upon  the  inner  circumference  of  the  rim. 
This  is  precisely  what  takes  place  on  the  earth  itself  where 
there  is  no  variation  ;  but  when  there  is  variation  either  of  di- 
rection or  of  dip,  i.e.,  a  disordering  of  the  proper  magnetic 
revolution  for  causes  later  to  be  set  forth,  then  there  is  some 
difference.  The  quadrant  described  on  the  block  must  be 
near  the  limb  of  the  terrella,  or  its  centre  must  be  at  the  limb 
itself,  and  the  needle  must  be  very  short  so  as  not  to  touch 


288  WILLIAM  GILBERT. 

the  terrella ;  for  there  is  error  when  the  needle  is  long  or 
placed  at  a  distance,  as  it  has  a  truly  proportionate  movement 
only  at  the  superficies  of  the  terrella.  But  were  the  quadrant 
— being  remote  from  the  terrella — to  be  moved  into  its  sphere 
of  influence  toward  the  pole  on  a  circle  concentric  with  the 
terrella,  then  the  needle  would  indicate  on  the  quadrant  the 
degrees  of  dip  in  ratio  and  symmetry  with  that  circle,  not  with 
the  terrella. 


CHAPTER  IV. 

OF  A  SUITABLE  LENGTH  OF  NEEDLE  ON  THE  TERRELLA  FOR 
SHOWING  THE  DIP. 

When  it  is  sought  to  define  the  dip  by  means  of  a  dip- 
indicating  instrument  on  the  earth  itself,  we  may  use  either  a 
short  versorium  or  one  ever  so  long,  provided  only  the  mag- 
netic property  of  the  loadstone  with  which  it  has  been  stroked 
is  able  to  pervade  its  whole  substance  and  length.  For  the 
greatest  length  of  a  versorium,  as  compared  with  the  earth's 
diameter,  is  insignificant  and  has  no  ratio  perceptible  by  sense. 
But  on  a  terrella,  or  on  a  plane  nigh  a  meridian  of  a  terrella,  a 
short  needle  is  required,  one  barley-corn's  length  ;  for  longer 
versoria  (because  they  reach  farther),  in  the  first  degrees  of  dip, 
descend  suddenly  and  irregularly,  and  turn  to  the  body  of  the 
terrella.  For  example,  as  soon  as  the  long  versorium  in  the 
figure  is  moved  onward  from  the  equator  A  to  C,  it  lays  hold 
of  the  stone  with  its  point  C  as  though  with  a  long  outspread 
wing,  when  the  point  reaches  the  parts  around  B,  which  give 
it  a  greater  revolution  than  those  at   C.     And   the  ends  of 


DIP  NOT  CAUSED  BY  ATTRACTION  OF  LOADSTONE.  289 

rather  long  pieces  of  wire  or  little  rods  are  also  made  to  rotate 
irregularly,  just  as  pieces  of  iron  wire  and  iron  balls  and  other 
spherical  loadstones  are  made  to  rotate  irregularly  by  an  ob- 
long loadstone  not  rounded  into  a  ball.     Yet  magnetic  bodies 


or  pieces  of  iron  on  the  surface  of  a  terrella  should  not  have  a 
long  but  a  very  short  axis,  so  that  they  may  dip  true  and  nat- 
urally ;  for  a  long  versorium  situated  near  a  terrella  does  not 
easily  stand  in  a  right  sphere  on  the  horizon,  and  wavers  and 
suddenly  dips  to  one  side  or  the  other,  especially  its  magnet- 
ized end,  or,  if  both  ends  are  magnetized,  then  the  end  mag- 
netized last. 


CHAPTER  V. 

THAT  DIP  IS  NOT  CAUSED  BY  THE  ATTRACTION  OF  A  LOAD- 
STONE, BUT  BY  ITS  POWER  OF  GIVING  DIRECTION  AND 
ROTATION. 

Throughout  nature  we  have  to  recognize  that  wondrous 
work  of  the  Maker  whereby  the  principal  bodies  are  restricted 
within  particular  localities  and,  as  it  were,  hedged  round  with 
fences,  nature  so  ordering.  Hence  it  is  that  heavenly  bodies 
do  not  get  confused  in  their  motions  and  in  their  progressions 


290  WILLIAM  GILBERT. 

beyond  each  other.  Similarly  are  the  magnetic  revolutions 
produced  by  the  force  of  a  greater  and  dominant  body  as  well 
as  by  that  of  a  lesser  and  subject  body,  though  that  be  of  very 
small  volume.  For  the  work  is  not  done  by  attraction  but  by 
incitation  on  the  part  of  both,  and  that  with  a  proportionate 
movement  toward  fixed  points  beyond  which  there  is  no  further 
motion.  For  did  the  versorium  dip  under  the  action  of  an  at- 
tractive force,  then  a  terrella  fashioned  out  of  a  very  powerful 
loadstone  would  pull  it  to  itself  more  than  would  one  made  of 
an  indifferent  loadstone,  and  iron  stroked  by  a  strong  loadstone 
would  have  greater  dip ;  but  that  is  never  so.  Further,  a  piece 
of  iron  attached  to  and  projecting  from  the  terrella  at  any  lati- 
tude does  not  cause  a  little  iron  bar  to  rise  more  to  perpendic- 
ular than  does  the  unarmed  stone,  though  when  so  armed  the 
stone  does  seize  and  lift  far  heavier  weights.  But  if  a  load- 
stone be  somewhat  fashioned  to  a  point  at  one  end,  and  rather 
obtuse  at  the  other,  the  acute  end  or  pole  solicits  with  greater 
force  magnetized  iron,  the  obtuse,  thick  end  makes  the  iron 
turn  to  itself  more  powerfully ;  but  a  spherical  stone  makes  it 
*turn  to  itself  powerfully  and  in  true  direction  according  to 
magnetic  laws  and  the  form  of  spheres ;  while  a  loadstone  of 
some  length  from  pole  to  pole  stirs  the  versorium  unequally, 
for  in  such  a  stone  the  pole  of  the  versorium  always  is  pointed 
toward  the  pole  of  the  loadstone  itself.  So,  too,  if  the  load- 
stone take  a  disk  shape,  with  the  poles  in  the  circumference, 
but  with  the  body  plane  and  not  spherical,  when  the  plane  is 
brought  near  to  the  versorium,  the  versorium  does  not  move 
with  the  regular  magnetic  movement  as  with  a  terrella,  but 
turns  round  always  pointing  toward  the  pole  of  the  loadstone 
situated  in  the  circumference  of  the  plane.  Besides,  if  the 
stone  caused  the  versorium  to  revolve  by  attraction,  then  in 
the  first  degrees  of  latitude  it  would  attract  toward  the  mass 


DTP  NOT  CAUSED  BY  ATTRACTION  OF  LOADSTONE,  29I 

of  the  terrella  itself  the  end  of  a  short  versorium  ;  but  it  does 
not  so  attract  as  to  bring  the  two  together  and  into  coition — 
the  versorium  simply  revolves  so  far  as  nature  demands,  as  is 
shown  in  the  following  instance. 


For  here  the  point  of  a  versorium  in  a  low  latitude  neither 
touches  the  stone  nor  comes  into  coition  with  it,  only  inclines 
toward  it.  Further,  when  the  versorium  rotates  as  it  dips,  the 
pole  of  the  versorium  is  not  stayed  nor  held  by  the  pole  of  the 
earth  or  the  terrella,  but  revolves  regularly,  nor  remains  in  any 
point  or  terminus,  nor  looks  straight  to  the  pole  toward  which 
the  centre  of  the  versorium  advances,  save  at  the  pole  itself, 
and  that  only  once  between  the  pole  and  the  equator ;  but  the 
inclination  goes  on  according  as  the  change  in  the  site  of  the 
centre  produces  a  dip  in  conformity  to  magnetic  laws.  The 
dip  of  the  needle  in  water,  demonstrated  in  the  sequel,  is  also 
constant :  the  needle  does  not  dip  toward  the  bottom  of  the 
vessel,  but  stands  in  mid  direction  poised  on  its  centre  accord- 
ing to  its  due  dip  ;  yet  this  would  not  be  the  case  if  the  earth 
or  its  poles  by  attraction  made  the  extremity  of  the  needle  to 
dip. 


292  WILLIAM  GILBERT. 


CHAPTER  VI. 

OF  THE  RATIO  OF  DIP    TO   LATITUDE  AND  THE  CAUSES 

THEREOF. 

We  have  spoken  of  the  construction  of  the  instrument  for 
determining  the  dip,  of  the  causes  and  modes  of  the  dip,  and  of 
the  different  incHnations  of  the  needle  for  different  locaHties; 
of  the  inclination  of  the  loadstone,  too,  and  of  an  instrument 
for  showing  the  power  of  the  stone  at  any  latitude,  as  well  as 
of  the  demonstrated  rotation  (by  erection)  of  pieces  of  iron  on 
a  meridian  of  the  stone,  according  to  latitude.  We  have  now 
to  treat  more  at  length  of  the  causes  of  this  proportionate 
inclination.  A  loadstone  and  a  piece  of  iron  wire,  when  moved 
in  a  meridian  from  the  equator  to  the  pole,  turn  toward  a 
spherical  loadstone,  and  toward  the  earth  also,  with  a  circular 
motion.  In  a  right  horizon  (as  also  upon  the  equinoctial  circle 
of  the  stone)  the  axis  of  the  iron,  which  is  its  middle,  is  a  line 
parallel  with  the  earth's  axis.  When  that  axis  reaches  the  pole, 
which  is  its  centre,  it  stands  still  in  the  same  right  line  with 
the  earth's  axis.  The  same  end  of  the  iron  that  at  the  equator 
points  south  turns  to  the  north ;  for  it  is  not  a  movement  of 
centre  to  centre,  but  of  one  magnetic  body  to  another,  and  a 
natural  turning  of  the  axis  of  the  body  to  the  axis  of  the 
terrella,  not  caused  by  the  pole's  attraction,  so  that  the  iron 
should  regard  the  earth's  polar  point.  On  the  equator  the 
magnetic  iron  stands  in  horizontal  equilibrium,  but  toward  the 
pole  on  either  side  of  the  equator,  at  every  latitude  from  the 


RATIO  OF  DIP    TO  LATITUDE. 


293 


beginning  of  the  first  degree  even  to  the  goth,  it  dips;  yet, 
not  in  ratio  to  the  number  of  degrees  or  the  arc  of  the  latitude 
does  the  magnetic  needle  dip  so  many  degrees  or  over  a  like 
arc ;  but  over  a  very  different  one,  for  this  movement  is  in 
truth  not  a  dipping  movement,  but  really  a  revolution  move- 
ment, and  it  describes  an  arc  of  revolution  proportioned  to 
the  arc  of  latitude.      Hence  the  magnetic  body  Ay  while  it 


passes  round  the  earth,  or  an  earthkin  or  terrella,  from  the 
equinoctial  circle  G  toward  B  (the  pole),  rotates  on  its  centre, 
and,  midway  in  its  progress  from  the  equator  to  pole  B^  points 
to  the  equator  F  as  the  mean  of  the  two  poles:  therefore 
ought  the  versorium  to  rotate  much  more  quickly  than  the 
centre  travels  in  order  to  regard  the  point  i^  in  a  right  line  by 
rotating.  For  this  reason  the  movement  of  this  rotation  is 
quick  in  the  first  degrees  from  the  equator,  from  A  to  Z,  but 
slower  in  the  subsequent  degrees,  from  L  to  B,  that  is,  with 
reference  to  the  equatorial  point  /%  toward  C  {in  respectibus  ab 
cequatore  F  ad  C).  But  were  dip  equal  to  the  latitude,  i.e., 
always  so  many  degrees  from  the  horizon  as  the  centre  of  the 


294 


WILLIAM  GILBERT. 


versorium  has  gone  away  from  the  equator,  then  the  magnetic 
needle  would  obey  the  potency  and  the  peculiar  virtue  of  the 
centre  as  a  point  operating  of  itself ;  but  it  obeys  the  whole 
and  its  mass  and  outer  limits,  the  powers  of  both  cooperating, 
*to  wit,  those  of  the  magnetized  versorium  and  of  the  earth. 


EXPLANATION  OF  DIAGRAM  OF  ROTATION.  295 


CHAPTER  VII. 

EXPLANATION  OF  THE  DIAGRAM  OF  THE  ROTATION  OF 
MAGNETIZED   IRON. 

Let  ACDL  be  the  body  of  the  earth  or  of  a  terrella,  M 
the  centre,  AD  the  equator,  CL  the  axis,  AB  the  horizon, 
which  changes  according  to  the  locahty.  From  the  point  F 
in  the  horizon,  at  a  distance  from  the  equator  A  equal  to  the 
semi-diameter  CM  of  earth  or  terrella,  is  described  an  arc  to 
H  as  terminus  of  the  quadrants  of  dip :  for  all  quadrants  of 
dip  that  belong  {inserviunt)  to  the  parts  between  A  and  C 
begin  at  that  arc  and  terminate  in  the  earth's  centre,  M.  The 
semi-diameter  of  this  arc  is  a  chord  drawn  from  the  equator 
A  to  the  pole  C.  And  a  line  equal  to  that  chord,  drawn  in 
the  horizon  to  B,  gives  the  starting  point  {principium)  of  the 
arc  of  the  termini  of  the  arcs  of  revolution  and  rotation,  which 
arc  is  continued  on  to  G.  For  as  the  quadrant  of  a  circle 
around  the  earth's  centre  (the  starting-point  of  it  being  in  the 
horizon,  at  a  distance  from  the  equator  equal  to  the  earth's 
semi-diameter)  is  the  terminus  of  all  the  quadrants  of  dip  pro- 
duced from  every  horizon  to  the  centre,  so  a  circle  round  the 
centre  from  the  starting  point  of  the  first  arc  of  rotation  B  to 
G  is  the  terminus  of  the  arcs  of  rotation.  Between  the  arc  of 
rotation  BL  and  BG  are  intermediate  arcs  of  revolution  and 
rotation  of  the  magnetic  needle.  The  centre  of  the  arc  is  the 
region  or  place  where  the  observation  is  obtained ;  the  begin- 
ning of  the  arc  is  taken  from  the  circle  that  is  terminus  of  the 
revolutions,  and  it  ends  at  the  opposite  pole,  as  from  O  to  Z, 


296  WILLIAM  GILBERT. 

in  45  degrees  latitude.  Divide  any  arc  of  revolution  into  90 
equal  parts  from  the  terminus  of  the  arcs  of  revolution  to  the 
pole ;  for  whatever  the  degree  of  latitude  of  the  place,  that 
part  of  the  arc  of  revolution  is  to  be  reckoned  as  cognominal 
to  it  which  the  magnetic  pole  in  rotating  upon  or  around 
terrella  or  earth  regards :  in  the  large  diagram  that  follows, 
this  is  indicated  by  the  right  lines.  In  the  middle  latitude  of 
45  degrees  the  magnetic  rotation  is  directed  to  the  equator, 
and  there  also  the  arc  from  its  terminus  to  the  pole  is  the 
quadrant  of  a  circle;  but  at  latitudes  above  this  {ante  hunc,\.&.y 
nearer  the  equator)  all  the  arcs  of  revolution  are  greater  than 
a  quadrant ;  in  latitudes  below  this  {post  hunc,  i.e.,  higher, 
farther  from  the  equator)  they  are  less :  in  the  former  the 
needle  rotates  quickly ;  in  the  latter  it  gradually  rotates  more 
slowly.  Each  region  has  its  own  arc  of  revolution,  in  which 
is,  according  to  the  number  of  the  degree  of  latitude  of  the 
place,  the  terminus  toward  which  the  needle  turns ;  so  that  a 
right  line  drawn  from  the  region  to  a  point  in  that  arc  cog- 
nominal  to  the  number  of  the  degree  of  latitude  indicates  the 
magnetic  direction,  and  shows  the  degree  of  the  inclination  at 
the  intersection  of  the  quadrant  of  dip  that  belongs  {inservit) 
to  the  given  region.  Take  away  the  arc  of  the  quadrant  of 
dip  from  the  centre  to  the  line  of  magnetic  direction,  and 
what  remains  is  the  arc  of  dip  beneath  the  horizon.  Thus,  in 
the  rotation  of  the  versorium  N,  whose  line  of  magnetic  direc- 
tion extends  to  D,  take  away  from  the  quadrant  of  dip  SM 
its  arc  RM,  and  what  remains  will  be  the  arc  of  dip,  that  is,  it 
shows  how  much  the  needle  dips  in  latitude  45  degrees- 


DIAGRAM  OF   THE  ROTATION  OF  MAGNETIZED  IRON.  297 


CHAPTER  VIII. 

DIAGRAM  OF  THE  ROTATION  OF  MAGNETIZED  IRON,  SHOW- 
ING THE  MAGNETIC  DIP  IN  ALL  LATITUDES,  AND  SHOW- 
ING THE  LATITUDE  FROM  THE  ROTATION  AND   DIP. 

In  the  foregoing  diagram,  around  the  body  of  the  earth  or 
of  the  terrella  are  drawn  a  circle  of  rotation  and  a  circle  of 
dip,  together  with  a  first,  a  last,  and  a  middle  arc  of  rotation 
and  dip.  Now  from  each  one  fifth  part  of  that  arc  which 
terminates  all  the  arcs  of  rotation  (and  each  of  which  also  is 
supposed  to  be  divided  into  90  equal  parts)  are  drawn  arcs  to 
the  pole,  and  from  every  fifth  degree  of  the  arc  terminating 
the  quadrants  of  dip  are  drawn  quadrants  to  the  centre,  and 
at  the  same  time  is  drawn  a  spiral  line  indicating  (by  the  aid 
of  a  movable  quadrant)  the  dip  in  every  latitude.  Right  lines 
of  magnetic  direction  are  drawn  from  the  degrees  marked  on 
the  meridian  of  earth  or  terrella  to  their  proper  arcs  and  to 
the  parts  answering  to  those  arcs. 

How  to  ascertain  the  elevation  of  the  pole,  or  the  latitude  of 
any  place,  by  means  of  the  following  diagram,  turned  into  a  mag- 
netic instrument,  in  any  part  of  the  world,  without  the  help  of 
the  heavenly  bodies,  sun,  planets,  or  fixed  stars,  and  in  foggy 
weather  as  well  as  in  darkness. 

We  can  see  how  far  from  idle  is  the  magnetic  philoso- 
phy; on  the  contrary,  how  delightful,  how  beneficial,  how 
divine !  Seamen  tossed  by  the  waves  and  vexed  with  incessant 
storms,  while  they  cannot  learn  even  from  the  heavenly  lumi- 
naries aught  as  to  where  on  earth  they  are,  may  with  the  great- 


298 


WILLIAM  GILBERT. 


est  ease  gain  comfort  from  an  insignificant  instrument,  and 
ascertain  the  latitude  of  the  place  where  they  happen  to  be. 
With  a  dip  instrument  an  observation  is  taken  of  the  degree  of 
the  needle's  dip  beneath  the  horizon ;  that  degree  is  noted  on 


the  inside  arc  of  the  quadrant,  and  the  quadrant  is  turned  round 
at  the  centre  of  the  instrument  until  that  degree  on  the  quad- 
rant touches  the  spiral  line :  then  in  the  open  space  B,  at  the 
centre  of  the  quadrant,  the  latitude  of  the  region  on  the  pe- 
riphery of  the  globe  is  found  by  the  linea  fiducics  AB.  Draw 
the  diagram  on  a  suitable  planed  board,  and  to  its  centre  attach 


DIAGRAM  OF   THE  ROTATION  OF  MAGNETIZED  IRON.  299 

the  centre  of  the  angle  of  the  quadrant  A^  so  that  the  quad- 
rant may  rotate  on  that  centre.  But  it  must  be  remembered 
also  that  in  some  places  there  is  variation  in  dip  for  the  causes 
aforesaid  (albeit  the  variation  is  not  great) :  this  variation  also 
it  will  be  well  to  study,  and  to  account  for  on  some  probable 


hypothesis,  and  it  will  be  of  very  great  interest  to  observe  it  in 
different  localities,  for  this  variation  of  dip  seems  to  present 
more  difficulty  than  the  variation  of  direction  ;  but  it  is  readily 
understood  with  dip  instruments  when  it  disagrees  either  by 
plus  or  by  minus  with  the  diagram. 


300  WILLIAM  GILBERT. 

Observing'  the  magnetic  dip  at  sea. 

Place  the  dip  instrument  upon  our  variation  instrument,  a 
wooden  ball  being  put  between  the  round  movable  compass- 
box  and  the  dip  instrument ;  but  first  remove  {eximitd)  the  verso- 
rium,  lest  it  interfere  with  the  dip  instrument.  In  this  way, 
when  the  sea  is  in  commotion  the  compass  box  will  remain 
erect  on  the  level  of  the  horizon.  The  dip  compass  is  to  be 
directed,  by  means  of  a  small  versorium  at  its  base,  to  the  point 
of  the  variation,  to  the  greater  circle  of  which  (commonly  called 
the  magnetic  meridian)  the  plane  of  the  upright  compass  con- 
forms ;  thus  the  dip  instrument,  in  virtue  of  its  property  of 
rotating,  shows  the  degree  of  the  dip. 

In  a  dip  instrument  the  -magnetic  needle  which  when  on  a 
meridian  circle  descends,  hangs  perpendicular  when  it  lies  on  a 
parallel. 

The  magnetic  needle,  in  due  position,  while  it  conforms 
itself  to  the  earth  in  virtue  of  its  rotatory  property,  dips  in  an 
oblique  sphere  to  a  certain  extent.  But  when  the  plane  of  the 
instrument  is  removed  from  the  plane  of  the  meridian,  the 
needle  (which  tends  poleward)  no  longer  remains  in  the  degree 
of  its  dip,  but  inclines  more  toward  the  centre,  for  the  direc- 
tional force  is  greater  than  that  of  the  dip ;  and  all  power  of 
dip  is  taken  away  if  the  plane  of  the  instrument  be  on  a 
parallel.  For  then  the  needle,  its  axis  being  transverse,  cannot 
take  its  due  position,  and  so  tends  perpendicular  to  earth,  and 
remains  only  in  its  own  meridian,  or  in  what  is  commonly 
called  the  magnetic  meridian. 


DEMONSTRATION  OF  DIRECTION.  301 


CHAPTER  IX. 

DEMONSTRATION  OF  DIRECTION,  OR  OF  VARIATION  FROM 
THE  TRUE  DIRECTION,  TOGETHER  WITH  DIP,  SIMPLY 
BY  THE  MOVEMENT  IN  WATER,  DUE  TO  THE  POWER 
OF  CONTROLLING  AND  ROTATING. 

Pass  through  a  round  cork  three  finger-breadths  of  thin  iron* 
wire,  so  that  the  cork  may  support  the  iron  in  water.  Let  the 
water  be  contained  in  a  vase  or  large  goblet  of  glass.  With  a 
very  sharp  knife  pare  the  cork  away  gradually  (still  preserving 
its  rotundity)  till  it  will  stand  a  finger-breadth  or  two  under 
the  surface  motionless,  with  the  wire  evenly  balanced.  Then 
stroke  one  end  of  the  wire  on  the  north  pole  of  a  loadstone, 
the  other  end  on  the  south  pole  (very  carefully,  so  that  the  cork 
may  not  be  moved  ever  so  little  out  of  its  place),  and  put  the 
instrument  again  in  the  water.  The  wire  will  dip  with  a  cir- 
cular movement  on  its  centre  below  the  plane  of  the  horizon, 
according  to  the  latitude  of  the  place,  and  even  as  it  dips  will 
show  (the  true  direction  being  disordered)  the  point  of  varia- 
tion. The  loadstone  with  which  it  is  rubbed  should  be  a 
powerful  one,  such  as  is  required  in  all  magnetic  demonstra- 
tions. When  the  wire  having  been  thus  put  in  the  water,  and 
treated  with  the  loadstone,  comes  to  a  standstill  in  the  line  of 
the  dip,  its  lower  end  remains  in  the  point  of  variation  in  an 
arc  of  a  great  circle,  or  meridian,  passing  through  the  zenith 
and  the  point  of  variation  in  the  horizon,  and  through  that 
lowermost  point  of  the  heavens  called  nadir :  all  this  is  demon- 
strated by  bringing   a   rather   long   magnetized   needle   near 


302  WILLIAM  GILBERT. 

the  vessel  on  one  side.  This  is  a  demonstration  of  the  absolute 
conforming  of  a  magnetic  body  to  unity  with  the  earth's  body ; 
here  in  the  natural  way  is  manifested  direction  with  variation 
thereof  and  dip.     But  it  is  to  be  understood  that  delicate  and 


difficult  as  this  experiment  is,  so  it  does  not  continue,  for  the 
apparatus  does  not  remain  in  the  midst  of  the  water,  but  at 
last  sinks  to  the  bottom  when  the  cork  has  taken  in  too  much 
water.^ 


1"  It  is  also  manifest  in  a  needle  pierced  through  a  globe  of  cork  so  cut 
away  and  pared  by  degrees  that  it  will  swim  under  water,  yet  sink  not  unto 
the  bottom,  which  may  be  well  effected  ;  for  if  the  cork  be  a  thought  too  light 
to  sink  under  the  surface,  the  body  of  the  water  may  be  attenuated  with  spirits 


VARIATION  OF  DIP.  303 


CHAPTER  X. 

OF  VARIATION    OF   DIP. 

We  have  already  spoken  of  direction  and  of  variation  as  a» 
sort  of  derangement  of  direction.  Now  we  observe  a  like 
irregular  movement  in  the  dip,  when  it  descends  beneath  the 
limits  or  when,  as  sometimes  happens,  it  does  not  reach  its  due 
bounds.  Thus  the  variation  of  the  dip  is  an  arc  of  the  mag- 
netic meridian  betwixt  the  true  and  the  apparent  dip.  For  as, 
because  of  elevations  of  the  earth,  magnetized  bodies  are  pulled 
to  one  side,  so,  too,  the  needle  (its  rotation  being  a  little  in- 
creased) dips  beyond  the  due  measure.  And  as  variation  is 
a  deviation  in  direction,  so,  for  the  same  reason,  there  is  some 
error  of  dip,  albeit  usually  a  trifling  one.  Sometimes,  too, 
though  there  be  no  variation  of  direction  on  the  horizon,  there 
may  nevertheless  be  a  variation  of  the  dip,  to  wit,  when  either 
in  a  direct  meridian  line,  i.e.,  on  the  meridian  itself,  there  pro- 
jects some  magnetically  powerful  earthmass,  or  when  such  ele- 
vations have  less  force  than  is  called  for  by  the  general  con- 


of  wine  ;  if  too  heavy,  it  may  be  incrassated  with  salt  ;  and  if  by  chance  too 
much  be  added,  it  may  again  be  thinned  by  a  proportionable  addition  of  fresh 
water.  If  then  the  needle  be  taken  out,  actively  touched  and  put  in  again,  it 
will  depresse  and  bow  down  its  Northern  head  toward  the  bottom,  and  ad- 
vance its  Southern  extremity  toward  the  brim.  This  way  invented  by  Gilbertus 
may  seem  of  difficulty  ;  the  same  with  lesse  labour  may  be  observed  in  a 
needled  sphere  of  cork  equally  contiguous  unto  the  surface  of  the  water  ;  for  if 
the  needle  be  not  exactly  equiponderant,  that  end  which  is  a  thought  too  light, 
if  touched  becometh  even  ;  that  needle  also  which  will  but  just  swim  under 
water,  if  forcibly  touched,  will  sink  deeper  and  sometime  unto  the  bottom" 
(Dr.  Thos.  Brown,  Pseudoloxia  Epidemica,  1658,  Book  II,  page  67). 


304  WILLIAM  GILBERT. 

stitution  of  the  globe,  or  when  the  energy  is  overconcentrated 
in  one  part,  and  in  another  is  diffused,  as  we  may  see  in  the 
Atlantic  Ocean.  And  this  discrepancy  of  constitution,  this 
variance  of  effect,  we  easily  recognize  in  certain  parts  of  every 
spherical  loadstone.  The  inequality  of  force  in  the  various 
regions  of  a  terrella  is  shown  by  the  conclusive  experiment 
described  in  Chapter  2  of  this  Book.  And  the  effect  is  clearly 
shown  by  the  demonstrational  {pstensivum)  instrument,  an 
account  of  which  is  contained  in  Chapter  3  of  the  same  Book, 


CHAPTER  XL 

OF  THE  FORMAL  MAGNETIC  ACT  SPHERICALLY  EFFUSED. 

*  Repeatedly  we  have  spoken  of  the  poles  of  earth  and 
terrella  and  of  the  equinoctial  circle  ;  last  we  treated  of  the  dip 
of  magnetized  bodies  earthward  and  terrellaward,  and  the 
causes  thereof.  But  having  with  divers  and  manifold  con- 
trivances labored  long  and  hard  to  get  at  the  cause  of  this  dip, 
we  have  by  good  fortune  discovered  a  new  and  admirable 
science  of  the  spheres  themselves — a  science  surpassing  the 
marvels  of  all  the  virtues  magnetical.  For  such  is  the  prop- 
erty of  magnetic  spheres  that  their  force  is  poured  forth  and 
diffused  beyond  their  superficies  spherically,  the  form  being 
exalted  above  the  bounds  of  corporeal  nature ;  and  the  mind 
that  has  diligently  studied  this  natural  philosophy  will  dis- 
cover the  definite  causes  of  the  movements  and  revolutions. 
The  potencies  of  a  terrella,  too,  are  of  the  same  kind  through- 
out the  whole  sphere  of  its  influence,  and  the  spheres  (of  influ- 
ence) themselves,  at  whatever  distance  from  the  body  of  the 


FORMAL  MAGNETIC  ACT  SPHERICALLY  EFFUSED.     305 

terrella,  have,  in  the  ratio  of  their  diameter  and  the  quantity 
of  their  superficies,  termini  of  their  forces,  or,  in  other  words,^ 
there  are  points  whereat  magnetic  bodies  turn  toward  them  ; 
and  these  bodies  do  not  regard  the  same  part  or  point  of  the 
terrella  at  every  distance  whatever  therefrom  (unless  they  be 
in  the  axis  of  the  spheres  and  the  terrella),  but  ever  do  tend 
toward  those  points  of  the  spheres  (of  influence)  which  are 
equal  arcs  distant  from  their  common  axis.  Thus  in  the 
following  diagram  we  show  the  body  of  a  terrella,  with  its 
poles  and  equator ;  also  a  magnetic  needle  in  three  other  con- 
centric spheres  around  the  terrella  and  at  some  distance  there- 
from. In  these  spheres  (and  they  may  be  imagined  as  infinite) 
the  magnetic  needle  or  versorium  regards  its  own  sphere  in 
which  it  is  placed  and  its  diameter,  poles,  and  equator,  not 
those  of  the  terrella ;  and  it  is  by  these  and  in  accordance  with 
the  magnitude  of  these  that  it  is  made  to  rotate  and  is  directed, 
both  while  its  centre  stands  still  and  while  it  advances  in  any 
arc  whatever  of  that  sphere.  Still  we  do  not  mean  that  the 
magnetic  forms  and  spheres  exist  in  the  air,  or  water,  or  any 
other  medium  not  magnetical,  as  though  the  air  or  water  took 
them  on  or  were  by  them  informated ;  for  the  forms  are  only 
effused  and  really  subsist  when  magnetic  bodies  are  present : 
hence  the  magnetic  body  within  the  forces  and  limits  of  the 
spheres  is  taken  hold  of,  and  in  the  several  spheres  magnetic 
bodies  control  other  bodies  magnetical  and  excite  them  even 
as  though  the  spheres  of  influence  were  solid  materiate  load- 
stones ;  for  the  magnetic  force  does  not  proceed  through  the 
whole  of  the  medium,  nor  exists  really  as  in  a  continuous 
body ;  and  so  the  spheres  are  magnetical,  and  yet  are  not  real 
spheres  existing  by  themselves. 

AB  is  the  axis  of  a  terrella  and  its  spheres ;  CD  the  equa- 
tor.    In  all  the  spheres,  as  on  the  terrella,  at  the  equator  the 


306 


WILLIAM  GILBERT. 


versorium  lies  in  the  plane  of  the  horizon ;  in  the  axis  it 
everywhere  regards  the  centre  perpendicularly ;  in  the  mid 
spaces,  E  regards  D,  and  G  regards  H,  not  i%  which  is  re- 


DlAGRAM   OF   THE   MOVEMENTS   IN   THE   MAGNETIC   SPHERES. 

garded  by  the  versorium  L  on  the  superficies  of  the  terrella. 
But  as  is  the  proportion  oi  L  \.o  F  on  the  terrella's  superficies, 
such  is  that  ol  G  to  H  in  its  own  sphere,  and  oi  E  to  D  in  its 
own  sphere ;  so  all  the  revolutions  in  the  spheres  to  the  ter- 
mini of  the  spheres  are  such  as  are  the  revolutions  at  the  sur- 


FORMAL  MAGNETIC  ACT  SPHERICALLY  EFFUSED.     307 

face  of  the  terrella  or  to  its  termini.  But  if  in  the  more  distant 
spheres  there  is  now  and  then  some  error,  that  is  to  be  charged 
to  the  inertia  of  the  loadstone  or  to  weakened  power,  because 
of  the  too  great  distance  of  the  spheres  from  the  terrella. 

DEMONSTRATION. 

Upon  the  instrumental  diagram  above  described,  place,  a 
small  board  or  a  strong  disk  of  brass  or  tin  on  which  are  in- 
scribed the  magnetic  spheres,  as  in  the  diagram  ;  and  in  the 
middle  make  a  hole  proportioned  to  the  size  of  the  terrella,  so 
that  the  board  may  lie  evenly  on  the  middle  of  it  along  the 
meridian  circle  above  the  wood.  Then  in  one  of  the  spheres 
of  influence  place  a  small  versorium  one  barley-corn  long ;  the 
versorium,  as  it  there  moves  into  various  positions  in  the  same 
circle,  will  always  have  regard  to  the  dimensions  of  that  sphere 
and  not  those  of  the  terrella,  as  is  seen  in  the  diagram  of  the 
effused  magnetic  forms.  While  some  writers  posit  as  causes 
of  the  wonderful  effects  of  the  loadstone  occult  and  recondite 
virtues  of  things,  and  others  regard  a  property  of  the  load- 
stone's substance  as  the  cause,  we  have  discovered  the  primary 
substantial  form  not  in  some  more  or  less  probable  foreshad- 
owing of  truth  or  in  reasons  that  admit  of  controversy ;  but  as 
in  many  other  demonstrations,  so  in  this  most  indisputable  dia- 
gram of  the  forces  magnetical  effused  by  the  form,  we  grasp 
the  true  efficient  cause.  And  this  (the  form),  though  it  is 
subject  to  none  of  our  senses  and  is  therefore  less  perceptible 
to  the  intellect,  now  appears  manifest  and  visible  before  our 
very  eyes  through  this  formal  act,  which  proceeds  from  it  as 
light  proceeds  from  a  source  of  light.  And  here  it  is  to  be 
noted  that  a  magnetic  needle  moved  over  the  earth,  or  over  a 
terrella,  or  over  the  effused  spheres,  rotates  completely  twice 
in  one  circuit  of  its  centre,  like  an  epicycle  round  its  circle. 


308  WILLIAM  GILBERT. 


CHAPTER  XII. 

THE  MAGNETIC  FORCE  IS  ANIMATE,  OR  IMITATES  A  SOUL; 
IN  MANY  RESPECTS  IT  SURPASSES  THE  HUMAN  SOUL 
WHILE  THAT  IS   UNITED  TO   AN   ORGANIC   BODY. 

Wonderful  is  the  loadstone  shown  in  many  experiments 
to  be,  and,  as  it  were,  animate.  And  this  one  eminent  prop- 
erty is  the  same  which  the  ancients  held  to  be  a  soul  in  the 
heavens,  in  the  globes,  and  in  the  stars,  in  sun  and  moon.  For 
they  deemed  that  not  without  a  divine  and  animate  nature 
could  movements  so  diverse  be  produced,  such  vast  bodies 
revolve  in  fixed  times,  or  potencies  so  wonderful  be  infused 
into  other  bodies  ;  whereby  the  whole  world  blooms  with  most 
beautiful  diversity  through  this  primary  form  of  the  globes 
themselves.  The  ancient  philosophers,  as  Thales,  Heraclitus, 
Anaxagoras,  Archelaus,  Pythagoras,  Empedocles,  Parmenides, 
Plato  and  all  the  Platonists,— nor  Greek  philosophers  alone,  but 
also  the  Egyptian  and  Chaldean, — all  seek  in  the  world  a  cer- 
tain universal  soul,  and  declare  the  whole  world  to  be  endowed 
with  a  soul.  Aristotle  held  that  not  the  universe  is  animate, 
but  the  heavens  only ;  his  elements  he  made  out  to  be  inani- 
mate ;  but  the  stars  were  for  him  animate.  As  for  us,  we  find 
this  soul  only  in  the  globes  and  in  their  homogenic  parts,  and 
albeit  this  soul  is  not  in  all  globes  the  same  (for  that  in  the  sun 
or  in  certain  stars  is  much  superior  to  that  in  other  less  noble 
globes).  Still  in  very  many  globes  the  souls  agree  in  their 
powers.  Thus,  each  homogenic  part  tends  to  its  own  globe 
and  inclines  in  the  direction  common  to  the  whole  world,  and 


MAGNETIC  FORCE  IS  ANIMATE.  3O9 

in  all  globes  the  effused  forms  reach  out  and  are  projected  in 
a  sphere  all  round,  and  have  their  own  bounds — hence  the 
order  and  regularity  of  all  the  motions  and  revolutions  of  the 
planets,  and  their  circuits,  not  pathless,  but  fixed  and  deter- 
minate, wherefore  Aristotle  concedes  to  the  spheres  and 
heavenly  orbs  (which  he  imagines)  a  soul,  for  the  reason  that 
they  are  capable  of  circular  motion  and  action  and  that  they 
move  in  fixed,  definite,  tracks.  And  I  wonder  much  why  the 
globe  of  earth  with  its  effluences  should  have  been  by  him 
and  his  followers  condemned  and  driven  into  exile  and  cast 
out  of  all  the  fair  order  of  the  glorious  universe,  as  being 
brute  and  soulless.  In  comparison  with  the  whole  creation 
'tis  a  mere  mite,  and  amid  the  mighty  host  of  many  thousands 
is  lowly,  of  small  account,  and  deformate.  And  to  it  the 
Aristotelians  add  allied  elements  that  by  like  ill-fortune  are 
also  beggarly  and  despicable.  Thus  Aristotle's  world  would 
seem  to  be  a  monstrous  creation,  in  which  all  things  are  per- 
fect, vigorous,  animate,  while  the  earth  alone,  luckless  small 
fraction,  is  imperfect,  dead,  inanimate,  and  subject  to  decay. 
On  the  other  hand,  Hermes,  Zoroaster,  Orpheus,  recognize  a 
universal  soul.  As  for  us,  we  deem  the  whole  world  animate, 
and  all  globes,  all  stars,  and  this  glorious  earth,  too,  we  hold  to 
be  from  the  beginning  by  their  own  destinate  souls  governed 
and  from  them  also  to  have  the  impulse  of  self-preservation. 
Nor  are  the  organs  required  for  organic  action  lacking,  whether 
implanted  in  the  homogenic  nature  or  scattered  through  the 
homogenic  body,  albeit  these  organs  are  not  made  up  of 
viscera  as  animal  organs  are,  nor  consist  of  definite  members; 
indeed  in  some  plants  and  shrubs  the  organs  are  hardly  recog- 
nizable, nor  are  visible  organs  essential  for  life  in  all  cases. 
Neither  in  any  of  the  stars,  nor  in  the  sun,  nor  in  the  planets 
that  are  most  operant  in  the  world,  can  organs  be  distinguished 


310  WILLIAM  GILBERT. 

or  imagined  by  us ;  nevertheless,  they  live  and  endow  with 
life  small  bodies  at  the  earth's  elevated  points.  If  there  is 
aught  of  which  man  may  boast,  that  of  a  surety  is  soul,  is 
mind ;  and  the  other  animals,  too,  are  ennobled  by  soul ;  even 
God,  by  whose  rod  all  things  are  governed,  is  soul.  But  who 
shall  assign  organs  to  the  divine  intellects,  seeing  that  they  are 
superior  to  all  organ-structure,  nor  are  comprised  in  material 
organs  ?  But  in  the  bodies  of  the  several  stars  the  inborn 
energy  works  in  ways  other  than  in  that  divine  essence  which 
presides  over  nature ;  and  in  the  stars,  the  sources  of  all 
things,  in  other  ways  than  in  animals;  finally,  in  animals  in 
other  ways  than  in  plants.  Pitiable  is  the  state  of  the  stars, 
abject  the  lot  of  earth,  if  this  high  dignity  of  soul  is  denied 
them,  while  it  is  granted  to  the  worm,  the  ant,  the  roach,  to 
plants  and  morels ;  for  in  that  case  worms,  roaches,  moths, 
were  more  beauteous  objects  in  nature  and  more  perfect,  inas- 
much as  nothing  is  excellent,  nor  precious,  nor  eminent,  that 
hath  not  soul.  But  since  living  bodies  spring  from  earth  and 
sun  and  by  them  are  animate,  and  since  in  the  earth  herbage 
springs  up  without  sowing  of  seeds  (e.g.,  when  soil  is  taken 
out  of  the  bowels  of  the  earth  and  carried  to  some  great  eleva- 
tion or  to  the  top  of  a  lofty  tower  and  there  exposed  to  the 
sunshine,  after  a  little  while  a  miscellaneous  herbage  springs 
up  in  it  unbidden),  it  is  not  likely  that  they  (sun  and  earth) 
can  do  that  which  is  not  in  themselves ;  but  they  awaken 
souls,  and  consequently  are  themselves  possessed  of  souls. 
Therefore  the  bodies  of  the  globes,  as  being  the  foremost 
parts  of  the  universe,  to  the  end  they  might  be  in  themselves 
and  in  their  state  endure,  had  need  of  souls  to  be  conjoined  to 
them,  for  else  there  were  neither  life,  nor  prime  act,  nor  move- 
ment, nor  unition,  nor  order,  nor  coherence,  nor  conactus,  nor 
sympathia^  nor  any  generation,  nor  alternation  of  seasons,  and 


MA  GNE  TIC  FOR  CE  IS  A  NIMA  TE  311 

no  propagation;  but  all  were  in  confusion  and  the  entire 
world  lapse  into  chaos,  and,  in  fine,  the  earth  were  void  and 
dead  and  without  any  us,e.  But  only  on  the  superficies  of  the 
globes  is  plainly  seen  the  host  of  souls  and  of  animate  exist- 
ences, and  in  their  great  and  dehghtful  diversity  the  Creator 
taketh  pleasure.  But  the  souls  (in  the  interior  of  the  globes) 
confined,  as  it  were,  by  prison  bars  send  not  forth  their  effused 
immaterial  forms  beyond  the  limits  of  the  body,  nor  are  bodies 
put  in  motion  by  them  without  labor  and  exertion ;  a  breath 
carries  and  bears  them  forth ;  but  if  that  breath  be  fouled  or 
stilled  by  mischance,  the  bodies  lie  like  the  world's  recrement 
or  as  the  waste  matter  of  the  globes.  But  the  globes  them- 
selves remain  and  endure,  rotate  and  move  in  orbits,  and 
without  wasting  or  weariness  run  their  courses.  The  human 
soul  uses  reason,  sees  many  things,  investigates  many  more  ; 
but,  however  well  equipped,  it  gets  light  and  the  beginnings  of 
knowledge  from  the  outer  senses,  as  from  beyond  a  barrier — 
hence  the  very  many  ignorances  and  foolishnesses  whereby 
our  judgments  and  our  life-actions  are  confused,  so  that  few 
or  none  do  rightly  and  duly  order  their  acts.  But  the  earth's 
magnetic  force  and  the  formate  soul  or  animate  form  of  the 
globes,  that  are  without  senses,  but  without  error  and  without 
the  injuries  of  ills  and  diseases,  exert  an  unending  action, 
quick,  definite,  constant,  directive,  motive,  imperant,  harmoni- 
ous, through  the  whole  mass  of  matter  ;  thereby  are  the  gen- 
eration and  the  ultimate  decay  of  all  things  on  the  superficies 
propagated.  For  if  it  were  not  for  the  movement  whereby  the 
daily  revolution  is  accomplished,  all  things  here  on  earth  were 
wild  and  disordered,  and  worse  than  desert  and  unused  would 
they  ever  remain.  Yet  these  movements  in  nature's  founts 
are  not  produced  by  thoughts  or  reasonings  or  conjectures, 
like  human  acts,  which  are  contingent,  imperfect,  and  indeter- 


312 


WILLIAM  GILBERT. 


minate,  but  connate  in  them  are  reason,  knowledge,  science, 
judgment,  whence  proceed  acts  positive  and  definite  from  the 
very  foundations  and  beginnings  of  the  world :  these,  because 
of  the  weakness  {imbecillitaie7n)  of  our  soul,  we  cannot  com- 
prehend. Wherefore,  not  without  reason,  Thales,  as  Aristotle 
reports  in  his  book  De  Anima,  declares  the  loadstone  to  be 
animate,  a  part  of  the  animate  mother  earth  and  her  beloved 
offspring. 


BOOK  VI. 


CHAPTER   I. 


OF  THE  GLOBE  OF  EARTH  AS  A  LOADSTONE. 


Hitherto  we  have  spoken  of  the  loadstone  and  magnetic 
bodies,  how  they  conspire  together  and  act  on  each  other, 
and  how  they  conform  themselves  to  the  terrella  and  to  the 
earth.  Now  we  have  to  treat  of  the  globe  of  earth  itself  sep- 
arately. All  the  experiments  that  are  made  on  the  terrella, 
to  show  how  magnetic  bodies  conform  themselves  to  it,  may 
— at  least  the  principal  and  most  striking  of  them — be  shown 
on  the  body  of  the  earth  ;  to  the  earth,  too,  all  magnetized 
bodies  are  associate.  And  first,  on  the  terrella  the  equinoctial 
circle,  the  meridians,  parallels,  the  axis,  the  poles,  are  natural 
limits:  similarly  on  the  earth  these  exist  as  natural  and  not 
merely  mathematical  limits.  As  on  the  periphery  of  a  terrella 
a  loadstone  or  the  magnetic  needle  takes  direction  to  the  pole, 
so  on  the  earth  there  are  revolutions  special,  manifest,  and 
constant,   from  both  sides  of  the  equator :   iron   is  endowed 

313 


314  WILLIAM  GILBERT. 

with  verticity  by  being  stretched  toward  the  pole  of  the  earth 
as  toward  the  pole  of  a  terrella;  again,  by  being  laid  down 
and  suffered  to  grow  cool  lying  toward  the  earth's  pole,  after 
its  prior  verticity  has  been  destroyed  by  fire,  it  acquires  new 
verticity  conformed  to  the  position  earthward.  And  iron  rods 
that  have  for  a  long  time  lain  in  the  poleward  direction  acquire 
verticity  simply  by  regarding  the  earth ;  just  as  the  same  rods, 
if  they  be  pointed  toward  the  pole  of  a  loadstone,  though  not 
touching  it,  receive  polar  force.  There  is  no  magnetic  body 
that  draws  nigh  in  any  way  to  a  loadstone  which  does  not  in 
hke  manner  obey  the  earth.  As  a  loadstone  is  more  powerful 
at  one  end  and  at  one  side  of  the  equator,  so  the  same  thing 
is  shown  with  a  small  terrella  on  a  large  one.  According  to 
the  difference  in  amount  and  mode  of  friction  in  magnetizing 
a  piece  of  iron  at  a  terrella,  it  will  be  powerful  or  weak  in  per- 
forming its  functions.  In  movements  toward  the  body  of  the 
earth,  just  as  on  a  terrella,  variation  is  produced  by  unlikeness 
and  inequality  of  prominences  and  by  imperfections  of  the 
surface;  and  all  variation  of  the  versorium  or  the  mariner's 
compass  all  over  the  earth  and  everywhere  at  sea — a  thing 
that  has  so  bewildered  men's  minds — is  found  and  recognized 
through  the  same  causes.  The  dip  of  the  magnetic  needle 
(that  wonderful  turning  of  magnetic  bodies  to  the  body  of  the 
terrella  by  formal  progression)  is  seen  also  in  the  earth  most 
clearly.  And  that  one  experiment  reveals  plainly  the  grand 
magnetic  nature  of  the  earth,  innate  in  all  the  parts  thereof 
and  diffused  throughout.  The  magnetic  energy,  therefore, 
exists  in  the  earth  just  as  in  the  terrella,  which  is  a  part  of 
the  earth  and  homogenic  in  nature  with  it,  but  by  art  made 
spherical  so  it  might  correspond  to  the  spherical  body  of  the 
'  earth  and  be  in  agreement  with  the  earth's  globe  for  the  capi- 
tal experiments. 


EARTH'S  MAGNETIC  AXIS  INVARIABLE.  315 


CHAPTER  II. 

THE   MAGNETIC   AXIS   OF    THE   EARTH    REMAINS   INVARIABLE. 

The  earth's  magnetic  axis,  just  as  it  passed  through  the  mid- 
earth  in  the  very  beginnings  of  the  moving  world,  so  to-day- 
tends  through  the  centre  to  the  same  points  of  the  superficies, 
the  equinoctial  line  and  plane  also  persisting  the  same.  For  not, 
save  with  a  vast  demolition  of  the  terrestrial  mass,  may  these 
natural  bounds  be  altered,  as  is  easily  shown  by  magnetic  dem- 
onstrations. Wherefore  the  opinion  held  by  Dominicus  Maria 
of  Ferrara,  a  man  of  rare  ability,  and  who  was  the  preceptor  of 
Nicolaus  Copernicus,  is  to  be  rejected.  It  was  based  on  cer- 
tain observations,  and  was  as  follows:  "Some  years  ago,"  he 
writes,  "  while  considering  Ptolemy's  geography,  I  found  the 
elevations  of  the  north  pole  given  by  him  for  the  several 
regions  to  fall  short  by  one  degree  and  ten  minutes  of  what 
they  are  in  our  time,  which  difference  can  by  no  means  be 
referred  to  an  error  of  the  table,  for  it  is  not  credible  that  the 
whole  book  should  be  throughout  equally  wrong  in  the  figures 
contained  in  the  tables  ;  therefore  we  must  suppose  the  north 
pole  brought  toward  the  vertical  point.  Thus  a  protracted 
observation  began  to  disclose  to  us  things  hid  from  our  ances- 
tors— not  through  any  sloth  on  their  part,  but  because  they 
lacked  observation  of  a  long  period  by  their  predecessors. 
For  very  few  places  before  Ptolemy's  time  were  observed  in 
elevations  of  the  pole,  as  he  himself  testifies  in  the  beginning 
of  his  Cosmographia :  '  Hipparchus  alone,'  he  writes,  'hath 
handed  down  to  us  the  latitudes  of  a  few  places ;  but  many 


3l6  WILLIAM  GILBERT. 

latitudes  of  distances,  especially  of  distances  to  east  and  west, 
have  been  fixed  on  a  basis  of  general  tradition,  and  this  is  not 
from  any  indolence  of  writers,  but  because  they  were  unac- 
quaint  with  a  more  accurate  mathematic/  Hence  it  is  no 
wonder  if  our  predecessors  have  not  noted  the  very  slow 
movement,  seeing  that  in  1700  years  it  has  advanced  about 
one  degree  toward  the  uttermost  point  of  human  habitation. 
This  is  shown  at  the  Strait  of  Gibraltar,  where  in  Ptolemy's 
day  the  north  pole  was  raised  36J  degrees  above  the  horizon, 
while  now  it  is  37f  degrees.  A  like  difference  is  shown  by 
Leucopetra  (Capo  dell'  Armi)  in  Calabria  and  sundry  other 
places  in  Italy,  namely,  places  that  have  not  changed  from 
Ptolemy's  time  to  ours.  Thus,  in  consequence  of  this  move- 
ment, places  that  now  are  inhabited  will  one  day  be  deserted, 
while  those  that  now  are  scorched  by  the  tropic  sun  will, 
albeit  after  a  long  time,  be  reduced  to  our  temperature.  For 
this  very  slow  movement  will  be  completed  in  395,cx)0  years." 
Thus,  according  to  Dominicus  Maria's  observations,  the 
north  pole  is  raised  higher  and  the  latitudes  of  places  are 
greater  now  than  in  the  past :  from  this  he  infers  a  change  of 
latitudes.  But  Stadius,  holding  the  directly  opposite  opinion, 
proves  by  observations  that  the  latitudes  have  grown  less. 
"  The  latitude  of  Rome,"  says  he,  "  is  given  in  the  Geographica 
of  Ptolemy  as  4if  degrees ;  and  lest  any  one  should  say  that 
some  error  has  crept  into  the  text  of  Ptolemy,  Pliny  relates,  and 
Vitruvius  in  his  ninth  book  testifies,  that  at  Rome  on  the  day 
of  the  equinox  the  ninth  part  of  the  gnomon's  shadow  is  lack- 
ing. But  recent  observation  (as  Erasmus  Rheinhold  states) 
gives  the  latitude  of  Rome  in  our  age  as  41^  degrees  ;  so  that 
you  are  in  doubt  whether  one  half  of  a  degree  has  been  lost 
{decrevisse)  in  the  centre  of  the  world,  or  whether  it  is  the  re- 
sult of  an  obliquation  of  the  earth."     From  this  we  may  see 


DAILY  MAGNETIC  REVOLUTION  OF   THE  GLOBES.     31/ 

how,  on  the  basis  of  inexact  observations,  men  conceive  new 
and  contrary  opinions  as  to  the  earth's  mechanism,  and  postu- 
late absurd  motions.  For,  as  Ptolemy  simply  took  from  Hip- 
parchus  a  few  latitudes  and  did  not  himself  observe  them  in 
many  places,  it  is  likely  that,  knowing  the  position  of  the 
countries,  he  made  a  conjectural  estimate  of  the  latitude  of 
cities,  and  set  such  conjectures  down  in  his  tables.  So,  here, 
in  Britain,  the  latitudes  of  cities  vary  two  or  three  degrees,  as 
we  know  by  experience.  Hence  no  new  movement  is  to  be 
postulated  on  the  ground  of  these  miscalculations,  nor  is  the 
grand  magnetic  nature  of  the  earth  to  be  deformed  for  the 
sake  of  a  judgment  so  rashly  arrived  at.  And  these  errors  have 
crept  into  geography  all  the  more  easily  because  the  mag- 
netic force  was  quite  unknown  to  authors.  Besides,  observa- 
tions of  latitudes  cannot  be  made  with  exactitude  save  by 
experts,  with  the  help  of  large  instruments,  and  by  taking 
account  of  refraction  of  lights. 


CHAPTER   III. 

OF  THE  DAILY  MAGNETIC  REVOLUTION  OF  THE  GLOBES,  AS 
AGAINST  THE  TIME-HONORED  OPINION  OF  A  primum 
mobile:   A  PROBABLE   HYPOTHESIS. 

Among  the  ancients,  Heraclides  of  Pontus,  and  Ecphantus, 
the  Pythagoreans  Nicetas  of  Syracuse  and  Aristarchus  of 
Samos,  and,  as  it  seems,  many  others,  held  that  the  earth 
moves,  that  the  stars  set  through  the  interposition  of  the 
earth,  and  that  they  rise  through  the  earth's  giving  way :   they 


3l8  WILLIAM  GILBERT. 

do  give  the  earth  motion,  and  the  earth  being,  like  a  wheel, 
supported  on  its  axis,  rotates  upon  it  from  west  to  east.  The 
Pythagorean  Philolaus  would  have  the  earth  to  be  one  of  the 
stars,  and  to  turn  in  an  oblique  circle  toward  the  fire,  just  as 
the  sun  and  moon  have  their  paths :  Philolaus  was  an  illus- 
trious mathematician  and  a  very  experienced  investigator  of 
nature.  But  when  Philosophy  had  come  to  be  handled  by 
many,  and  had  been  given  out  to  the  public,  then  theories 
adapted  to  the  capacity  of  the  vulgar  herd  or  supported  with 
sophistical  subtleties  found  entrance  into  the  minds  of  the 
many,  and,  like  a  torrent,  swept  all  before  them,  having  gained 
favor  with  the  multitude.  Then  were  many  fine  discoveries 
of  the  ancients  rejected  and  discredited — at  the  least  were  no 
longer  studied  and  developed.  First,  therefore,  Copernicus 
among  moderns  (a  man  most  worthy  of  the  praise  of  scholar- 
ship) undertook,  with  new  hypotheses,  to  illustrate  the  ph(E- 
nomena  of  bodies  in  motion ;  and  these  demonstrations  of 
reasons,  other  authors,  men  most  conservent  with  all  manner 
of  learning,  either  follow,  or,  the  more  surely  to  discover  the 
alleged  {(paiyo}A.eyj]v)  "symphony"  of  motion,  do  observe. 
Thus  the  suppositions  and  purely  imaginary  spheres  postulated 
by  Ptolemy  and  others  for  finding  the  times  and  periods  of 
movements,  are  not  of  necessity  to  be  accepted  in  the  physical 
lectures  of  philosophers. 

It  is  then  an  ancient  opinion,  handed  down  from  the  olden 
time,  but  now  developed  by  great  thinkers,  that  the  whole  earth 
makes  a  diurnal  rotation  in  the  space  of  twenty-four  hours. 
But  since  we  see  the  sun,  the  moon,  and  the  other  planets,  and 
the  whole  heavenly  host,  within  the  term  of  one  day  come  and 
depart,  then  either  the  earth  whirls  in  daily  motion  from  west 
to  east,  or  the  whole  heavens  and  all  the  rest  of  the  universe 
of  things  necessarily  speeds  about  from  east  to  west.     But  in 


DAILY  MAGNETIC  REVOLUTION  OF   THE   GLOBES.     319 

the  first  place,  it  is  not  probable  that  the  highest  heaven  and 
all  those  visible  splendors  of  the  fixed  stars  are  swept  round 
in  this  rapid  headlong  career.  Besides,  what  genius  ever  has 
found  in  one  same  (Ptolemaic)  sphere  those  stars  which  we 
call  fixed,  or  ever  has  given  rational  proof  that  there  are  any 
such  adamantine  spheres  at  all  ?  No  man  hath  shown  this 
ever ;  nor  is  there  any  doubt  that  even  as  the  planets  are  at 
various  distances  from  earth,  so,  too,  are  those  mighty  and 
multitudinous  luminaries  ranged  at  various  heights  and  at  dis- 
tances most  remote  from  earth :  they  are  not  set  in  any 
sphaeric  framework  or  firmament  (as  is  supposed),  nor  in  any 
vaulted  structure.  As  for  the  intervals  (between  the  spheres) 
imagined  by  some  authors,  they  are  matters  of  speculation, 
not  of  fact ;  those  other  intervals  do  far  surpass  them  and  are 
far  more  remote  ;  and,  situated  as  they  are  in  the  heavens,  at 
various  distances,  in  thinnest  aether,  or  in  that  most  subtile 
fifth  essence,  or  in  vacuity — how  shall  the  stars  keep  their 
places  in  the  mighty  swirl  of  these  enormous  spheres  composed 
of  a  substance  of  which  no  one  knows  aught  ?  Astronomers 
have  observed  1022  stars  ;  besides  these,  innumerable  other 
stars  appear  minute  to  our  senses  ;  as  regards  still  others,  our 
sight  grows  dim,  and  they  are  hardly  discernible  save  by  the 
keenest  eye ;  nor  is  there  any  man  possessing  the  best  power 
of  vision  that  will  not,  while  the  moon  is  below  the  horizon 
and  the  atmosphere  is  clear,  feel  that  there  are  many  more 
indeterminable  and  vacillating  by  reason  of  their  faint  Hght, 
obscured  because  of  the  distance.  Hence,  that  these  are  many 
and  that  they  never  can  be  taken  in  by  the  eye,  we  may  well 
believe.  What,  then,  is  the  inconceivably  great  space  between 
us  and  these  remotest  fixed  stars?  and  what  is  the  vast  im- 
measurable amplitude  and  height  of  the  imaginary  sphere  in 
which  they  are  supposed  to  be  set  ?     How  far  away  from  earth 


320  WILLIAM   GILBERT. 

are  those  remotest  of  the  stars :  they  are  beyond  the  reach  of 
eye,  or  man's  devices,  or  man's  thought.  What  an  absurdity 
is  this  motion  (of  spheres). 

It  is  evident,  therefore,  that  all  the  heavenly  bodies,  being, 
as  it  were,  set  down  in  their  destined  places,  in  them  are  con- 
globed  whatever  elements  bear  to  their  own  centres,  and 
around  them  are  assembled  all  their  parts.  But  if  they  have 
a  motion,  it  will  be  motion  of  each  round  its  proper  centre, 
like  the  earth's  rotation ;  or  it  will  be  by  a  progression  in  an 
orbit,  like  that  of  the  moon  ;  in  so  multitudinous  a  scattered 
flock  there  will  be  no  circular  motion.  And  of  the  stars,  those 
situate  nigh  the  equator  would  seem  to  be  borne  around  with 
greatest  rapidity,  while  others  nigher  the  pole  have  a  rather  less 
rapid  movement  ;  and  others  still,  as  though  motionless,  have 
but  a  small  revolution.  Yet  no  differences  in  the  light,  the 
mass,  or  the  colors  of  the  light  are  perceptible  for  us ;  for  they 
are  as  brilliant,  as  clear,  as  resplendent,  or  as  faint  (sombre, 
ftisccB)  toward  the  poles  as  nigh  the  equator  and  the  zodiac ; 
and  in  their  seats  do  they  remain  and  there  are  they  placed, 
nor  are  they  suspended  from  aught,  nor  fastened  nor  secured 
in  any  vault.  Far  more  extravagant  {jnsanior)  yet  is  the  idea 
of  the  whirling  of  the  supposititious  primum  mobile^  which  is 


'  Primum  mobile  (first  cause  of  motion),  name  given  jn  the  Ptolemaic 
System  to  the  imaginary  huge  outermost  sphere,  in  the  centre  of  which  stood 
the  earth,  and  by  the  revolutions  of  which  from  east  to  west  diurnal  motion 
was  given  to  all  the  heavens,  creating  the  phenomena  of  day  and  night.  Ac- 
cording to  Aristotle,  the  FIRST  heaven  was  that  of  the  Moon,  the  second  Mer- 
cury, THIRD  Venus,  FOURTH  the  Sun,  fifth  Mars,  sixth  Jupiter,  seventh 
Saturn,  and  the  eighth  that  of  the  fixed  stars.  Two  more  heavens  were  added 
by  later  theorists  :  a  ninth,  moving  slowly  round  the  poles  of  the  ecliptic  and 
carrying  the  entire  system  forward  in  longitude,  to  produce  the  phenomena 
arising  from  the  precession  of  the  equinoxes,  the  tenth  being  the  primum 
mobile  beyond  which  was  the  empyreal  heaven. 

"  It  was  the  errour  of  Aristotle,"  says  Hakewill,  "that  via  lactea  was  a 
meteor  ;  and  not  onely  of  Aristotle,  but  almost  all  before  him,  that  there  were 


DAILY  MAGNETIC  REVOLUTION  OF   THE   GLOBES.     32 1 

still  higher,  deeper,  more  immeasurable  ;  and  yet  this  incom- 
prehensible primum  mobile  would  have  to  be  of  matter,  of 
enormous  altitude,  and  far  surpassing  all  the  creation  below  in 
mass,  for  else  it  could  not  make  the  whole  universe  down  to 
the  earth  revolve  from  east  to  west,  and  we  should  have  to 
accept  a  universal  force,  an  unending  despotism,  in  the  govern- 
ance of  the  stars,  and  a  hateful  tyranny.  This  primum  mobile 
presents  no  visible  body,  is  in  no  wise  recognizable  ;  it  is  a 
fiction  believed  in  by  some  philosophers,  and  accepted  by 
weaklings  who  wonder  more  at  this  terrestrial  mass  here  than 
at  those  distant  mighty  bodies  that  baffle  our  comprehension. 
But  there  cannot  be  diurnal  motion  of  infinity  or  of  an 
infinite  body,  nor,  therefore,  of  this  immeasurable  primum 
mobile.  The  moon,  neighbor  of  earth,  makes  her  circuit  in 
twenty-seven  days ;  Mercury  and  Venus  have  a  tardy  move- 
ment ;  Mars  completes  his  period  in  two  years,  Jupiter  in 
twelve,  Saturn  in  thirty.  And  the  astronomers  who  ascribe 
motion  to  the  fixed  stars  hold  that  it  is  completed,  according 
to  Ptolemy,  in  36,000  years,  or,  according  to  Copernicus's 
observations,  in  25,816  years  ;  thus  in  larger  circles  the  motion 
and  the  completion  of  the  course  are  ever  more  slow  ;  and  yet 
this  primum  mobile^  surpassing  all  else  in  height  and  depth, 
immeasurable,  has  a  diurnal  revolution.     Surely  that  is  super- 

but  EIGHT  Celestiall  Spheres  ;  after  this  Timocaris,  about  330  years  B.C.,  found 
out  nine;  but  about  the  yeare  of  Christ  1250,  Alphonsus  discovered  ten,  and 
the  received  opinion  now  is  that  there  are  eleven,  the  highest  of  all  being  held 
immoveable,  the  seate  of  Angels  and  blessed  spirits." 

Tycho  Brahe  was  of  the  same  opinion  with  Ptolemy,  viz.,  that  the  earth  is 
at  rest  in  the  centre  of  the  world  and  that  the  whole  machine  of  the  heavens  is 
turned  about  it  from  east  to  west  in  the  space  of  a  day,  by  action  of  the 
primum  mobile  (Jacobi  Rohaulti,  Physica,  Londini  1718,  Par.  II,  Cap.  VIII 
and  XXIII,  or  Rohault's  "System  of  Nat.  Phil.,"  London  1728,  Vol.  II,  pages 
24,  58). 

As  is  well  known,  the  doctrine  of  a  fixed  central  earth  was  doomed  by  the 
brilliant  investigations  of  Galileo,  Kepler,  and  Newton. 


322  WILLI  A  AI  GILBERT. 

station,  a  philosophic  fable,  now  believed  only  by  simpletons 
and  the  unlearned  ;  it  is  beneath  derision ;  and  yet  in  times 
past  it  was  supported  by  calculation  and  comparison  of  move- 
ments, and  was  generally  accepted  by  mathematicians,  while 
the  importunate  rabble  of  philophasters  egged  them  on. 

The  motions  of  the  heavenly  bodies  (i.e.,  of  the  planets) 
seem  all  to  be  eastward,  and  according  to  the  succession  of  the 
zodiacal  signs  ;  and  mathematicians  and  philosophers  of  the 
vulgar  sort  do  also  believe  that  the  fixed  stars  progress  in  the 
same  way  with  a  very  slow  movement :  to  these  stars  they 
must  needs,  through  their  ignorance  of  the  truth,  add  a  ninth 
sphere.  But  now  this  ina.dmlssihlQ  prttmim  mobile^  this  fiction, 
this  something  not  comprehensible  by  any  reasoning  and  evi- 
denced by  no  visible  star,  but  purely  a  product  of  imagination 
and  mathematical  hypothesis,  accepted  and  believed  by  philos- 
ophers, and  reared  into  the  heavens  and  far  beyond  all  the 
stars, — this  must  needs  by  a  contrary  incitation  wheel  from 
east  to  west,  counter  to  the  tendence  of  all  the  rest  of  the 
universe. 

Whatever  in  nature  moves  naturally,  the  same  is  impelled 
by  its  own  forces  and  by  a  consentient  compact  of  other 
bodies.  Such  is  the  motion  of  the  parts  to  a  whole,  of  the 
globes  and  stars  throughout  the  universe  with  each  other 
accordant ;  such  is  the  circular  propulsion  of  the  planets' 
bodies,  each  the  other's  career  observing  and  inciting.  But  as 
regards  this  primum  mobile  with  its  contrary  and  most  rapid 
career, — where  are  the  bodies  that  incite  it,  that  propel  it? 
Where  is  the  nature  conspiring  with  it?  and  what  mad  force 
lies  beyond  the  primum  mobile  ? — for  the  agent  force  abides  in 
bodies  themselves,  not  in  space,  not  in  the  interspaces. 

But  he  who  supposes  that  all  these  bodies  are  idle  and  in- 
active, and  that  all  the  force  of  the  universe  pertains  to  those 


DAILY  MAGNETIC  REVOLUTION-  OF   THE   GLOBES.     323 

spheres,  is  as  foolish  {insanit)  as  the  one  who,  entering  a  man's 
residence,  thinks  it  is  the  ceilings  and  the  floors  that  govern 
the  household,  and  not  the  thoughtful  and  provident  good-man 
of  the  house.  So,  then,  not  by  the  firmament  are  they  borne, 
not  from  the  firmament  have  they  movement  or  position  ;  and 
far  less  are  those  multitudes  of  stars  whirled  round  en  masse 
by  the  primum  mobile,  and  taken  up  at  random  and  swept 
along  in  a  reversed  direction  at  highest  velocity. 

Ptolemy  of  Alexandria,  it  seems  to  me,  was  over-timid  and 
scrupulous  in  apprehending  a  break-up  of  this  nether  world 
were  earth  to  move  in  a  circle.  Why  does  he  not  apprehend 
universal  ruin,  dissolution,  confusion,  conflagration,  and  stu- 
pendous celestial  and  supercelestial  calamities  from  a  motion 
that  surpasses  all  imagination,  all  dreams  and  fables  and  poetic 
licenses — a  motion  ineffable  and  inconceivable  ?  So,  then,  we 
are  borne  round  and  round  by  the  earth's  daily  rotation — a 
more  congruous  sort  of  motion  ;  and  as  a  boat  glides  over  the 
water,  so  are  we  whirled  round  with  the  earth,  the  while  we 
think  we  stand  still  and  are  at  rest.  This  seems  to  some  phi- 
losophers wonderful  and  incredible,  because  of  the  ingrained 
belief  that  the  mighty  mass  of  the  earth  makes  an  orbital  move- 
ment in  twenty-four  hours :  it  were  more  incredible  that  the 
moon  should  in  the  space  of  twenty-four  hours  traverse  her 
orbit  or  complete  her  course ;  more  incredible  that  the  sun 
and  Mars  should  do  so ;  still  more  that  Jupiter  and  Saturn  ; 
more  than  wonderful  would  be  the  velocity  of  the  fixed  stars 
and  firmament ;  and  let  them  imagine  as  best  they  may  the 
wonders  that  confront  them  in  the  ninth  sphere.  But  it  is  ab- 
surd to  imagine  a  primum  mobile,  and,  when  imagined,  to  give 
to  it  a  motion  that  is  completed  in  twenty-four  hours,  denying 
that  motion  to  the  earth  within  the  same  space  of  time.  For 
a  great  circle  of  earth,  as  compared  to  the  circuit  of  the  primum 


324  WILLIAM  GILBERT. 

mobile  is  less  than  a  stadium'  as  compared  to  the  whole  earth. 
And  if  the  rotation  of  the  earth  seems  headlong  and  not  to  be 
permitted  by  nature  because  of  its  rapidity,  then  worse  than 
insane,  both  as  regards  itself  and  the  whole  universe,  is  the 
motion  of  the. pi'imwn  mobile,  as  being  in  harmony  or  propor- 
tion with  no  other  motion.  Ptolemy  and  the  Peripatetics 
think  that  all  nature  must  be  thrown  into  confusion,  and  the 
whole  structure  and  configuration  of  this  our  globe  destroyed 
by  the  earth's  so  rapid  rotation.  The  diameter  of  the  earth  is 
1 71 8  German  miles  ;  the  greatest  elongation  of  the  new  moon 
is  65,  the  least  55,  semi-diameters  of  the  earth;  but  probably 
its  orbit  is  still  larger.  The  sun  at  his  greatest  eccentricity  is 
distant  1 142  semi-diameters  from  earth  ;  Mars,  Jupiter,  Saturn, 
as  they  are  slow  in  movement,  so  are  far  more  distant  from  the 
earth.  The  best  mathematicians  regard  the  distances  of  the 
firmament  and  the  fixed  stars  as  indeterminable  ;  to  say  noth- 
ing of  the  ninth  sphere,  if  the  convexity  of  th.Qprtmum  mobile  be 
fairly  estimated  in  its  proportion  to  the  rest,  it  must  travel 
over  as  much  space  in  one  hour  as  might  be  comprised  within 
three  thousand  great  circles  of  the  earth,  for  on  the  convexity 
of  the  firmament  it  would  travel  over  more  than  eighteen 
hundred  such  circles :  but  w^hat  structure  of  iron  can  be 
imagined  so  strong,  so  tough,  that  it  would  not  be  wrecked  and 
shattered  to  pieces  by  such  mad  and  unimaginable  velocity  ? 
The  Chaldees  beheved  the  heavens  to  be  light.  But  in  light 
there  is  no  such  firmness,  neither  in  the  fire-firmament  of 
iPlotinus,  nor  in  the  fluid  or  watery  heavens  of  God-inspired 
Moses,  nor  in  the  supremely  tenuous  and  transparent  firma- 
ment that  stands  between  our  eye  and  the  lights  of  the  stars, 
but  does  not  intercept  the  same.     Hence  we  must  reject  the 

'  Stadium — ancient  measure  of  length,  equal  to  600  Greek  or  625  Romaa 
feet,  or  125  Roman  paces,  or  to  606  feet  9  inches  English. 


DAILY  MAGNETIC  REVOLUTION  OF   THE   GLOBES.     32$ 

deep-seated  error  about  this  mad,  furious  velocity,  and  this 
forceful  retardation  of  the  rest  of  the  heavens.  Let  the  theo- 
logues  reject  and  erase  these  old  wives'  stories  of  a  so  rapid 
revolution  of  the  heavens  which  they  have  borrowed  from  cer- 
tain shallow-  philosophers.  The  sun  is  not  swept  round  by 
Mars'  sphere  (if  sphere  he  have)  and  its  motion,  nor  Mars  by 
Jupiter's  sphere,  nor  Jupiter  by  Saturn's :  the  sphere  of  the 
fixed  stars,  too,  seems  moderate  enough,  save  that  movements 
are  attributed  to  the  heavens  that  really  are  earth  movements, 
and  these  produce  a  certain  change  in  the  phenomena.  The 
higher  do  not  tyrannize  over  the  lower,  for  the  heaven  both  of 
the  philosopher  and  of  the  divine  must  be  gentle,  happy, 
tranquil,  and  not  subject  to  changes  ;  neither  will  the  violence, 
fury,  velocity,  and  rapidity  of  the  primum  mobile  bear  sway. 
That  fury  descends  through  all  the  celestial  spheres  and  heav- 
enly bodies,  enters  the  elements  of  the  philosophers,  sweeps 
the  fire  along,  whirls  the  air  around,  or  at  least  the  greater  part 
thereof ;  leads  in  its  train  the  universal  ether,  and  causes  it  to 
whirl  round  as  though  it  were  a  solid  and  firm  body,  whereas 
it  is  a  most  tenuous  substance,  that  neither  offers  resistance  nor 
is  ductile  ;  and  leads  captive  the  fires  of  the  upper  heavens.  O 
wondrous  steadfastness  of  the  globe  of  earth,  that  alone  is 
unconquered !  And  yet  the  earth  is  holden  nor  stayed  in  its 
place  by  any  chains,  by  no  heaviness  of  its  own,  by  no  con- 
tiguity of  a  denser  or  a  more  stable  body,  by  no  weights. 
The  substance  of  the  terrestrial  globe  withstands  and  resists 
universal  nature, 

Aristotle  imagines  a  philosophy  of  motions  simple  or  com- 
plex, holds  that  the  heavens  move  with  a  simple  circular 
motion,  and  his  elements  with  motion  in  a  right  line ;  that  the' 
parts  of  the  earth  tend  to  the  earth  in  right  lines  ;  that  they 
impinge  upon  it  at  the  superficies  at  right  angles  and  seek  its 


32t5  WILLIAM  GILBERT. 

centre,  and  there  always  rest ;  and  that  hence  the  whole  earth 
stands  in  its  place,  held  together  and  compacted  by  its  own 
weight.  This  coherence  of  parts  and  this  consolidation  of 
matter  exists  in  the  sun,  the  moon,  the  planets,  the  fixed  stars, 
— in  short,  in  all  those  spherical  bodies  whose  parts  cohere  and 
seek  their  several  centres ;  else  would  the  heavens  rush  to  de- 
struction and  their  grand  order  disappear.  But  these  heavenly 
bodies  have  a  circular  motion,  and  hence  the  earth,  too,  may 
have  its  motion,  for  this  motion  is  not,  as  some  suppose,  ad- 
verse to  cohesion  nor  to  production.  For,  inasmuch  as  this 
motion  is  intrinsic  in  the  earth  and  natural,  and  as  there  is 
nothing  without  that  may  convulse  it  or  with  contrary  motions 
impede  it,  it  revolves  untroubled  by  any  ill  or  peril ;  it  moves 
on  under  no  external  compulsion ;  there  is  nought  to  make 
resistance,  nothing  to  give  way  before  it,  but  the  path  is  open. 
For  since  it  revolves  in  a  space  void  of  bodies,  the  incorporeal 
aether,  all  atmosphere,  all  emanations  of  land  and  water,  all 
clouds  and  suspended  meteors,  rotate  with  the  globe :  the 
space  above  the  earth's  exhalations  is  a  vacuum  ;  in  passing 
through  vacuum  even  the  lightest  bodies  and  those  of  least 
coherence  are  neither  hindered  nor  broken  up.  Hence  the 
entire  terrestrial  globe,  with  all  its  appurtenances,  revolves 
placidly  and  meets  no  resistance.  Causelessly,  therefore,  and 
superstitiously,  do  certain  faint-hearts  apprehend  collisions,  in 
the  spirit  of  Lucius  Lactantius,  who,  like  the  most  unlearned 
of  the  vulgar,  or  like  an  uncultured  bumpkin,  treats  with  ridicule 
the  mention  of  antipodes  and  of  a  round  globe  of  earth.* 


*  "  Yet  that  which  to  me  seemeth  more  strange,  is  that  those  two  learned 
Clearkes,  Lactantius  ('Divinarum  Institut.,'  31,  c.  24)  and  Augustine  (' D,e 
Civitat,  Dei,'  i.  16,  c,  9),  should  with  that  earnestnesse  deny  the  being  of  any 
Antipodes. . . .  Zachary,  Bishop  of  Rome,  and  Boniface,  Bishop  of  Mentz,  led 
(as  it  *eemes)  by  the  authority  of  these  Fathers,  \yen,t  farther  herein,  cosdetnfl- 


THE  EARTH  HATH  A   CIRCULAR  MOTION.  $2? 

From  these  arguments,  therefore,  we  infer,  not  with  mere 
probability,  but  with  certainty,  the  diurnal  rotations  of  the 
earth  ;  for  nature  ever  acts  with  fewer  rather  than  with  many 
means ;  and  because  it  is  more  accordant  to  reason  that  the 
one  small  body,  the  earth,  should  make  a  daily  revolution  than 
that  the  whole  universe  should  be  whirled  around  it.  I  pass 
by  the  earth's  other  movements,  for  here  we  treat  only  of  the 
diurnal  rotation,  whereby  it  turns  to  the  sun  and  produces  the 
natural  day  (of  twenty-four  hours)  which  we  call  nyctJiemeron. 
And,  indeed,  nature  would  seem  to  have  given  a  motion  quite 
in  harmony  with  the  shape  of  the  earth,  for  the  earth  being  a 
globe,  it  is  far  easier  and  far  more  fitting  that  it  should  revolve 
on  its  natural  poles,  than  that  the  whole  universe,  whose  bounds 
we  know  not  nor  can  know,  should  be  whirled  round ;  easier 
and  more  fitting  than  that  there  should  be  fashioned  a  sphere 
of  the  primum  mobile — a  thing  not  received  by  the  ancients, 
and  which  even  Aristotle  never  thought  of  or  admitted  as 
existing  beyond  the  sphere  of  the  fixed  stars ;  finally,  which 
the  holy  Scriptures  do  not  recognize,  as  neither  do  they  recog- 
nize a  revolution  of  the  whole  firmament. 


CHAPTER   IV. 

THAT  THE  EARTH  HATH  A  CIRCULAR  MOTION. 

And  now,  though  philosophers  of  the  vulgar  sort  imagine, 
with  an  absurdity  unspeakable,  that  the  whole  heavens  and  the 
world's  vast  magnitude  are    in  rotation,  it  remains  that  the 

ing  one  Virgilius,  a  Bishop  of  Saltzburg,  as  an  heretique,  only  for  holding  that 
there  were  antipodes"  (Dr.  Geo.  Hakewill,  "An  Apologie  . . . .,"  Oxford  1635, 
Lib.  Ill,  page  281). 


328  WILLIAM  GILBERT. 

earth  daily  makes  one  revolution  ;  for  in  no  third  mode  can  the 
apparent  revolutions  be  accounted  for.  The  day,  therefore, 
which  we  call  the  natural  day  is  the  revolution  of  a  meridian 
of  the  earth  from  sun  to  sun.  And  it  makes  a  complete  revolu- 
tion from  a  fixed  star  to  the  same  fixed  star  again.  Bodies 
that  by  nature  move  with  a  motion  circular,  equable,  and  con- 
stant, have  in  their  different  parts  various  metes  and  bounds. 
Now  the  earth  is  not  a  chaos  nor  a  chance  medley  mass,  but 
through  its  astral  property  has  limits  agreeable  to  the  circular 
motion,  to.  wit,  poles  that  are  not  merely  mathematical  expres- 
sions, an  equator  that  is  not  a  mere  fiction,  meridians,  too,  and 
parallels ;  and  all  these  we  find  in  the  earth,  permanent,  fixed, 
and  natural ;  they  are  demonstrated  with  many  experiments 
in  the  magnetic  philosophy.  For  in  the  earth  are  poles  set  at 
fixed  points,  and  at  these  poles  the  verticity  from  both  sides  of 
the  plane  of  the  equator  is  manifested  with  greatest  force 
through  the  co-operation  of  the  whole ;  and  with  these  poles 
the  diurnal  rotation  coincides.  But  no  revolutions  of  bodies, 
no  movements  of  planets,  show  any  sensible,  natural  poles  in 
the  firmament  or  in  2SiY  primum  mobile  ;  neither  does  any  argu- 
ment prove  their  existence ;  they  are  the  product  of  imagina- 
tion. We,  therefore,  having  directed  our  inquiry  toward  a  cause 
that  is  manifest,  sensible,  and  comprehended  by  all  men,  do 
know  that  the  earth  rotates  on  its  own  poles,  proved  by  many 
magnetical  demonstrations  to  exist.  For  not  in  virtue  only  of 
its  stability  and  its  fixed  permanent  position  does  the  earth 
possess  poles  and  verticity ;  it  might  have  had  another  direc- 
tion, as  eastward  or  westward,  or  toward  any  other  quarter. 
By  the  wonderful  wisdom  of  the  Creator,  therefore,  forces  were 
implanted  in  the  earth,  forces  primarily  animate,  to  the  end  the 
globe  might,  with  steadfastness,  take  direction,  and  that  the 
poles  might  be  opposite,  so  that  on  them,  as  at  the  extremities 


THE  EARTH  HATH  A    CIRCULAR  MOTION.  329 

of  an  axis,  the  movement  of  diurnal  rotation  might  be  per- 
formed. Now  the  steadfastness  of  the  poles  is  controlled  by 
the  primary  soul.  Thus  it  is  for  the  good  of  the  earth  that  the 
collimations  of  the  verticities  do  not  continually  regard  a  fixed 
point  in  the  firmament  and  in  the  visible  heavens.  For  the 
changes  of  the  equinoxes  are  caused  by  a  certain  inflection  of 
the  earth's  axis,  yet  in  this  inflection  the  earth  hath  from  her 
own  forces  a  steadfastness  in  her  motion.  In  her  rotation 
the  earth  bears  on  her  own  poles ;  for  since  the  verticity  is 
fixed  in  A  and  B,  and  the  axis  horizontal,  at  C  and  D 
(equinoctial  line)  the  parts  are  free,  all  the  forces  being  diffused 


on  both  sides  from  the  plane  of  the  equator  toward  the  poles 
in   the  asther,'   which   is  without  resistance,  or  in   vacuum ; 

*  Aether,  according  to  Sir  Isaac  Newton,  is  a  thin  subtile  matter  much 
finer  and  rarer  than  air.  Sometimes  it  is  termed  by  him  a  subtil  spirit,  as  in 
the  latter  part  of  his  Principia,  and  sometimes  a  subtil  astherial  medium,  as  in 
his  Optics.  By  many  it  is  supposed  to  pervade  all  space,  also  the  interior  of 
solid  bodies,  and  to  be  the  medium  of  the  transmission  of  light  and  heat.  The 
sether  of  Descartes  was  his  materia  subtilis  or  his  First  Element  ;  by  which  he 
understood  a  "most  subtil  matter  very  swiftly  agitated,  fluid,  and  keeps  to  no 
certain  figure,  but  which  suits  itself  to  the  figure  of  those  bodies  that  are  about 


330 


WILLIAM  GILBERT. 


and,  A  and  B  remaining  constant,  C  revolves  toward  D  both 
by  natural  conformity  and  fitness,  as  also  for  the  sake  of  a  nec- 
essary good  and  avoidance  of  ill,  but  most  of  all  because  the 
effused  spheres  of  solar  influence  and  of  solar  Hght  do  impel. 
And  it  revolves  not  in  a  new  track  or  one  assigned  from  with- 


out, but,  in  the  general  trend  of  all  the  rest  of  the  planets,  tends 
from  west  to  east.  For  all  planets  have  a  like  movement  to 
the  east,  in  accordance  with  the  succession  of  the  zodiacal 
signs,  whether  it  be  Mercury  or  Venus  within  the  sun's  orbit,  or 
whether  they  revolve  round  the  sun.     That  the  earth  is  fitted 

it."  His  Second  Element  consists  of  small  globules  ;  that  is,  bodies  exactly 
round  and  very  solid,  wiiich  do  not  only,  like  the  First  Element,  fill  up  the 
pores  of  bodies,  but  also  constitute  the  purest  substance  of  the  ^ther  and 
Heaven  (Blome's  translation  of  Descartes'  Philos.,  page  loi ;  R.  Lovett,  "The 
Subtil  medium  prov'd,"  London  1756,  pages  14,  15). 


THE  EARTH  HATH  A    CIRCULAR  MOTION.  33 1 

for  circular  movement  is  proved  by  its  parts,  which,  when  sepa- 
rated from  the  whole,  do  not  simply  travel  in  a  right  line,  as 
the  Peripatetics  taught,  but  rotate  also.  A  loadstone  placed 
in  a  wooden  vessel  is  put  in  water  so  that  it  may  float  freely, 
rotate,  and  move  about.  If  the  pole  B  of  the  loadstone  be 
made  to  point,  unnaturally,  toward  the  south  F,  the  terrella 
revolves  round  its  centre  in  a  circular  motion  on  the  plane  of 
the  horizon  toward  the  north  E,  where  it  comes  to  a  rest,  and 
not  at  C  or  at  D.  So  acts  a  small  stone  weighing  only  four 
ounces;  and  a  powerful  loadstone  of  100  pounds  will  make  the 
same  movement  as  quickly ;  and  the  largest  mountain  of  load- 
stone would  revolve  in  the  same  way  were  it  to  be  set  afloat 
on  a  wide  stream  or  in  the  deep  sea ;  and  yet  a  magnetic  body 
is  far  more  hindered  by  water  than  is  the  whole  earth  by  the 
air.  The  whole  earth  would  act  in  the  same  way,  were  the 
north  pole  turned  aside  from  its  true  direction  ;  for  that  pole 
would  go  back,  in  the  circular  motion  of  the  whole,  toward 
Cynosura. 

Yet  this  motion  is  nothing  by  that  circular  motion  where- 
with the  parts  naturally  tend  to  their  own  places.  The  whole 
earth  regards  Cynosura  by  its  steadfast  nature ;  and  similarly 
each  true  part  of  the  earth  seeks  a  like  place  in  the  world,  and 
turns  with  circular  motion  to  that  position.  The  natural  move- 
ments of  the  whole  and  of  the  parts  are  alike :  hence,  since  the 
parts  move  in  a  circle,  the  whole,  too,  hath  the  power  of  cir- 
cular motion.  A  spherical  loadstone,  when  floated  in  water, 
moves  circularly  on  its  centre  to  become  (as  it  seems)  con- 
formed to  the  earth  on  the  plane  of  the  equator.  Thus,  too, 
would  it  move  on  any  other  great  circle  if  it  were  free  to  move, 
so  that  in  the  dip  compass  there  is  circular  movement  on  the 
meridian  (if  there  be  no  variation),  or,  if  there  is  variation,  on 
a  great  circle  drawn  from  the  zenith  through  the  variation  point 


332 


WILLIAM  GILBERT, 


in  the  horizon.  And  this  circular  movement  of  the  loadstone 
to  its  true  and  natural  position  shows  that  the  whole  earth  is 
fitted,  and  by  its  own  forces  adapted  for  a  diurnal  circular  mo- 
tion. I  omit  what  Petrus  Peregrinus  so  stoutly  affirms,  that  a 
terrella  poised  on  its  poles  in  the  meridian  moves  circularly 
with  a  complete  revolution  in  twenty-four  hours.  We  have 
never  chanced  to  see  this  :  nay,  we  doubt  if  there  is  such  move- 


ment,* both  because  of  the  weight  of  the  stone  itself,  and  also 
because  the  whole  earth,  as  it  moves  of  itself,  so  is  propelled 
by  the  other  stars ;  but  this  does  not  occur  proportionately  in 
any  part  of  the  earth,  a  terrella  for  example.  The  earth  moves 
by  its  primary  form  and  natural  desire,  for  the  conservation, 
perfecting,  and  beautifying  of  its  parts,  toward  the  more  ex- 


'  Father  Nicolao  Cabeo  clearly  explains  what  Peregrinus  advanced,  in  Lib. 
Ill,  Cap.  IV,  of  his  Philosophia  Magnetica. 


THE  EARTH  HATH  A    CIRCULAR  MOTION.  333 

cellent  things :  this  is  more  probable  than  that  those  fixed 
luminous  orbs,  and  the  planets  and  the  sun,  foremost  of  all  and 
divine,  while  they  get  no  aid  of  any  sort  from  earth,  no  refresh- 
ment, no  force  whatever,  should  vainly  circle  round  it,  and  that 
the  whole  host  of  heaven  should  make  everlasting  rounds 
about  the  earth,  without  any  profit  whatever  to  those  stars 
themselves. 

The  earth  therefore  rotates,  and  by  a  certain  law  of  neces- 
sity, and  by  an  energy  that  is  innate,  manifest,  conspicuous, 
revolves  in  a  circle  toward  the  sun ;  through  this  motion  it 
shares  in  the  solar  energies  and  influences ;  and  its  verticity 
holds  it  in  this  motion  lest  it  stray  into  every  region  of  the  sky. 
The  sun  (chief  inciter  of  action  in  nature),  as  he  causes  the 
planets  to  advance  in  their  courses,  so,  too,  doth  bring  about 
this  revolution  of  the  globe  by  sending  forth  the  energies  of  his 
spheres — his  light  being  effused. 

And  were  not  the  earth  to  revoxve  with  diurnal  rotation, 
the  sun  would  ever  hang  with  its  constant  light  over  a  given 
part,  and,  by  long  tarrying  there,  would  scorch  the  earth,  re- 
duce it  to  powder,  and  dissipate  its  substance,  and  the  upper- 
most surface  of  earth  would  receive  grievous  hurt :  nothing  of 
good  would  spring  from  earth,  there  would  be  no  vegetation  ; 
it  could  not  give  life  to  the  animate  creation,  and  man  would 
perish.  In  other  parts  all  would  be  horror,  and  all  things  frozen 
stiff  with  intense  cold  :  hence  all  its  eminences  would  be  hard, 
barren,  inaccessible,  sunk  in  everlasting  shadow  and  unending 
night.  And  as  the  earth  herself  cannot  endure  so  pitiable  and 
so  horrid  a  state  of  things  on  either  side,  with  her  astral  mag- 
netic mind  she  moves  in  a  circle,  to  the  end  there  may  be,  by 
unceasing  change  of  light,  a  perpetual  vicissitude,  heat  and 
cold,  rise  and  decline,  day  and  night,  morn  and  even,  noonday 
and  deep  night.     So  the  earth  seeks  and  seeks  the  sun  again, 


334  WILLIAM  GILBERT. 

turns  from  him,  follows  him,  by  her  wondrous  magnetical 
energy. 

And  not  only  from  the  sun  would  ill  impend,  were  the 
earth  to  stand  still  and  be  deprived  of  the  benefit  of  his  rays ; 
from  the  moon  also  great  dangers  would  threaten.  For  we 
see  how  the  ocean  swells  and  comes  to  flood  under  certain 
positions  of  the  moon.  But  if  by  the  daily  rotation  of  the 
earth  the  moon  did  not  quickly  pass,  the  sea  would  rise  unduly 
at  some  parts  and  many  coasts  would  be  overwhelmed  by 
mighty  tides.  Lest  the  earth,  then,  should  in  divers  ways 
perish  and  be  destroyed,  she  rotates  in  virtue  of  her  magnetic 
and  primary  energy.  And  such  are  the  movements  in  the  rest 
of  the  planets,  the  motion  and  light  of  other  bodies  especially 
urging.  For  the  moon  also  turns  round  during  its  menstrual 
circuit  that  it  may  on  all  its  parts  successively  receive  the 
sun's  light,  which  it  enjoys,  with  which  it  is  refreshed  like  the 
earth  itself;  nor  could  the  moon  without  grave  ill  and  sure 
destruction  stand  the  unceasing  incidence  of  the  light  on  one 
of  its  sides  only. 

Thus  each  of  the  moving  globes  has  circular  motion,  either 
in  a  great  circular  orbit  or  on  its  own  axis  or  in  both  ways. 
But  that  all  the  fixed  stars,  and  the  planets,  and  all  the  higher 
heavens,  still  revolve  simply  for  the  earth's  sake  is  for  the 
mind  of  a  philosopher  a  ridiculous  supposition.  The  earth 
then  revolves,  and  not  the  whole  heavens ;  and  this  movement 
brings  growth  and  decay,  gives  occasion  for  the  generation  of 
animated  things,  and  arouses  the  internal  heat  to  productive- 
ness. Hence  does  matter  vegetate  to  receive  forms,  and  from 
this  primary  revolution  of  the  earth  natural  bodies  have  prime 
incitation  and  original  act.  The  motion  of  the  whole  earth, 
therefore,  is  primary,  astral,  circular  about  its  poles,  whose 
verticity  rises  on  both  sides  from  the  plane  of  the  equator,  and 


ARGUMENT  AGAINST  EARTH'S  MOTION— REFUTATION.    335 

the  energy  is  infused  into  the  opposite  ends,  so  that  the  globe 
by  a  definite  rotation  might  move  to  the  good,  sun  and  stars 
inciting.  But  the  simple  right-downward  motion  assumed  by 
the  Peripatetics  is  the  movement  of  weight,  of  coacervation, 
of  separated  parts,  m  the  ratio  of  their  matter,  by  right  lines 
toward  the  earth's  centre,  these  tending  to  the  centre  by  the 
shortest  route.  The  motions  of  separate  magnetical  parts  of 
the  earth  are,  besides  that  of  coacervation,  those  of  coition, 
revolution,  and  direction  of  the  parts  to  the  whole,  into  har- 
mony and  agreement  of  the  form. 


CHAPTER  V. 

ARGUMENTS    OF   THOSE    WHO    DENY    THE    EARTH'S   MOTION; 
AND   REFUTATION   THEREOF. 

It  will  not  be  superfluous  to  weigh  also  the  arguments  of 
those  who  deny  that  the  earth  moves,  to  the  end  we  may  the 
better  satisfy  the  herd  of  philosophers  who  deem  the  stead- 
fastness and  immobility  of  the  globe  to  be  proved  by  incon- 
trovertible arguments.  Aristotle  does  not  allow  that  the 
earth  moves  circularly,  for,  says  he,  then  every  part  thereof 
would  take  the  same  motion ;  but  inasmuch  as  all  separated 
parts  tend  to  the  middle  point  in  right  lines,  that  circular 
motion  were  something  imposed  by  force,  were  contrary  to 
nature,  were  not  perpetual.  But  we  have  already  proven  that 
all  true  parts  of  the  earth  do  move  circularly,  and  that  all 
magnetic  bodies  (when  fitly  arranged)  are  borne  round  in  a 
circle.     But  they  tend  to  the  earth's  centre  in  a  right  line  (if 


33^  WILLIAM  GILBERT. 

the  way  is  open)  by  the  motion  of  coacervation,  as  to  their 
origin ;  they  move  with  various  motions  to  conformation  of 
the  whole ;  a  terrella  moves  circulariy  by  its  inborn  forces. 
"Besides,"  says  Aristotle,  "all  things  that  move  in  a  circle 
seem  afterward  to  lose  the  first  movement  and  to  be  carried 
on  by  several  motions  other  than  the  first.  The  earth,  too, 
whether  situate  in  the  middle  or  near  the  middle  of  the  world, 
must  needs  have  two  movements ;  and  were  that  the  case 
there  must  needs  be  progressions  and  retrogressions  of  the 
fixed  stars :  no  such  thing  is  seen,  however,  but  evermore  the 
same  stars  are  rising  and  setting  in  the  same  places."  Yet  it 
by  no  means  follows  that  a  twofold  motion  is  attributed  to 
the  earth.  And  if  there  be  but  the  one  diurnal  motion  of  the 
earth  round  its  poles,  every  one  sees  that  the  stars  must 
always  rise  and  set  in  the  same  way,  at  the  same  points  of  the 
horizon,  even  though  there  be  another  movement  for  which 
we  are  not  contending ;  because  the  changes  in  the  smaller 
sphere  produce  in  the  fixed  stars  no  variation  of  aspect  on 
account  of  the  great  distance,  unless  the  earth's  axis  changes 
position  :  of  this  we  treat  in  the  chapter  treating  of  the  cause 
of  the  precession  of  the  equinoxes. 

In  this  reasoning  (of  Asritotle's)  are  many  flaws.  For  if  the 
earth  rotates,  that,  as  we  have  shown,  must  be  due  not  to  the 
action  of  the  first  sphere,  but  to  its  own  native  forces.  And  if 
the  motion  were  produced  by  the  first  sphere,  there  would  be 
no  alternations  of  days  and  nights,  for  the  globe  would  then 
make  her  revolution  along  with  the  primum  mobile.  And  it 
does  not  follow,  because  the  rest  of  the  heavenly  bodies  move 
with  a  twofold  motion,  that  the  earth  has  a  twofold  motion 
when  it  rotates  round  its  centre.  Then,  too,  Aristotle  does 
not  clearly  apprehend  the  reason  of  the  case,  nor  do  his  trans- 
lators either,     rovrov  de  crvjJL^aivovto^j  avayKaiov  yiyrecr- 


ARGUMENT  AGAINST  EARTH'S  MOTION— REFUTATION.  337 

Bai  TCapodors  Kai  rpoTrds  rcSv  evSede/xevcor  acrtpoov  (de 
Caelo,  Cap.  14) — i.e.,  if  that  be  so  there  must  needs  be  muta- 
tions and  regressions  of  the  fixed  stars.  Some  translate 
rpoTtas  "  regressions  "  or  "  retrogressions,"  others  "  diver- 
sions": these  terms  can  in  no  wise  be  understood  of  axial 
motion  unless  Aristotle  means  that  the  earth  is  whirled  by  the 
prhnum  mobile  round  other  poles  different  even  from  those  of 
the  first  sphere — which  is  quite  absurd. 

More  recent  writers  hold  that  the  Eastern  Ocean  must 
needs,  in  consequence  of  this  motion,  so  be  driven  toward  the 
regions  to  the  west  that  parts  of  the  earth  which  are  dry  and 
waterless  would  of  necessity  be  daily  submerged  beneath  the 
waters.  But  the  ocean  gets  no  impulsion  from  this  motion,  as 
there  is  no  resistance,  and  even  the  whole  atmosphere  is 
carried  round  also ;  for  this  reason,  in  the  rapid  revolution  of 
the  earth,  things  in  the  air  around  are  not  left  behind  nor  do 
they  have  the  appearance  of  moving  westward ;  the  clouds 
stand  motionless  in  the  atmosphere,  save  when  impelled  by 
the  force  of  the  winds  ;  and  objects  thrown  up  into  the  air  fall 
back  again  to  their  places.  B'lt  they  are  dullards  who  think 
that  steeples,  churches,,  and  ^thsr  edifices  must  necessarily  be 
shaken  and  topple  down  if  tne  earth  moves :  antipodes  might 
fear  lest  they  should  slip  over  to  the  other  side  of  the  globe ; 
navigators  might  dread  lest  in  making  the  circle  of  the  whole 
globe  they  might,  once  they  had  descended  below  the  plane  of 
our  horizon,  drop  down  into  the  opposite  part  of  the  sky. 
But  these  are  old-wives'  imaginings  and  ravings  of  philoso- 
phasters  who,  when  they  undertake  to  discourse  of  great 
things  and  the  fabric  of  the  world  and  attempt  aught,  are 
unable  to  understand  hardly  anything  ultra  crepidam.  The 
earth  they  hold  to  be  the  centre  of  a  circle  and  to  stand 
motionless  in  the   general   revolution.     But  the  stars  or  the 


338  WILLIAM  GILBERT. 

planetary  globes  do  not  move  in  a  circle  round  the  centre  of 
the  earth ;  nor  is  the  earth  the  centre — if  it  be  in  the  centre — 
but  a  body  around  the  centre. 

And  it  is  inconsistent  that  the  Peripatetics'  heavenly  bodies 
should  rest  on  so  frail,  so  perishable,  a  thing  as  the  earth's 
centre. 

Now  generation  results  from  motion,  and  without  motion 
all  nature  would  be  torpid.  The  sun's  motions,  the  moon's 
motions,  produce  changes  ;  the  earth's  motion  awakens  the 
inner  life  of  the  globe ;  animals  themselves  live  not  without 
motion  and  incessant  working  of  the  heart  and  the  arteries. 
As  for  the  single  motion  in  a  right  line  to  the  centre,  that  this 
is  the  only  movement  in  the  earth,  and  that  the  movement  of 
an  individual  body  is  one  and  single, — the  arguments  for  it 
have  no  weight,  for  that  motion  in  a  right  line  is  but  the  incli- 
nation toward  their  origin,  not  only  of  the  earth,  but  also  of  the 
parts  of  the  sun,  the  moon,  and  all  the  other  globes  ;  but  these 
move  in  a  circle  also.  Joannes  Costeus,  who  is  in  doubt  as  to 
the  cause  of  the  earth's  motion,  regards  the  magnetic  energy 
to  be  intrinsic,  active,  and  controlling ;  the  sun  he  holds  to  be 
an  extrinsic  promovent  cause ;  nor  is  the  earth  so  mean  and 
vile  a  body  as  it  is  commonly  reputed  to  be.  Hence,  according 
to  him,  the  diurnal  motion  is  produced  by  the  earth,  for  the 
earth's  sake  and  for  the  earth's  behoof. 

They  (if  such  there  be)  who  assert  that  this  movement  of 
the  earth  takes  place  not  only  in  longitude  but  also  in  latitude, 
speak  nonsense  ;  for  nature  has  set  in  the  earth  definite  poles 
and  has  established  definite  and  not  confused  revolutions. 
Thus  the  moon  turns  round  to  the  sun  in  its  monthly  course, 
the  while  ever  regarding  with  definite  poles  definite  parts  .of 
the  heavens.  It  were  absurd  to  suppose  that  the  atmosphere 
moves  the  earth  ;  for  the  air  is  but  exhalation  and  the  effluvium 


ARGUMENT  AGAINST  EARTH'S  MOTION— REFUTATION.   339 

of  the  earth  given  out  in  every  direction  ;  winds,  too,  are  only 
motions  of  the  exhalation  here  and  there  along  the  earth's  sur- 
face ;  the  depth  of  the  air  current  is  trifling,  and  there  are  in 
every  region  various  winds  from  different  and  opposite  points. 
Some  authors,  not  finding  the  cause  of  the  revolution  in  the 
earth's  matter — for  there  they  say  they  find  only  solidity  and 
consistence — maintain  that  it  is  not  to  be  found  in  the  form, 
and  will  admit  as  qualities  of  the  earth  only  cold  and  dryness, 
which  cannot  produce  the  earth's  motion.  The  Stoics  attribute 
to  the  earth  a  soul,  and  hence  they  declare,  amid  the  derision 
of  the  learned,  that  the  earth  is  an  animal.  This  magnetical 
form,  be  it  energy  or  be  it  soul,  is  astral.  Let  the  learned 
lament  and  weep  for  that  neither  the  early  Peripatetics,  nor 
the  common  run  of  philosophasters,  nor  Joannes  Costeus,  who 
mocks  at  this  sort  of  thing,  were  capable  of  appreciating  this 
grand  and  most  extraordinary  fact  of  nature.  As  for  the  ob- 
jection that  the  superficial  unevenness  produced  by  mountains 
and  valleys  would  prevent  diurnal  revolution,  it  is  of  no  weight ; 
for  mountains  do  not  mar  the  rotundity  of  the  earth — as  com- 
pared with  the  entire  earth,  mountains  are  but  trifling  excres- 
cences :  besides,  the  earth  does  not  rotate  without  carrying 
along  with  it  its  effluences.  Beyond  the  effluences  there  is  no 
resistance.  The  earth's  motion  is  performed  with  as  little  labor 
as  the  motions  of  the  other  heavenly  bodies :  neither  is  it 
inferior  in  dignity  to  some  of  these.  To  say  that  it  is  folly  to 
suppose  the  earth  is  more  eager  for  the  face  of  the  sun  than 
the  sun  for  the  face  of  the  earth,  is  mere  wilfulness  and  igno. 
ranee.  Of  the  cause  of  the  rotation  I  have  oft  spoken.  If  any 
one  were  to  look  for  the  cause  of  the  rotation  or  any  other 
tendency  of  the  earth  on  the  globe-encircling  ocean,  or  in  the 
movement  of  the  atmosphere,  or  in  the  heaviness  of  the  earth's 
mass,  he  would  reason  as  stupidly  as  do  those  who  obstinately 


340  WILLIAM  GILBERT. 

cling  to  an  opinion  because  it  was  held  by  the  ancients.  Ptol- 
emy's arguments  are  of  no  account ;  for  our  true  principles 
once  laid  down,  the  truth  is  visible,  and  it  is  useless  to  refute 
Ptolemy.  So  let  Costeus  and  the  philosophers  recognize  how 
inprofitable  and  vain  a  thing  it  is  to  take  their  stand  on  the 
Joctrines  and  unproved  theories  of  certain  ancient  writers. 
Many  persons  cannot  see  how  it  is  (if  the  earth  rotates)  that  a 
ball  of  iron  or  lead  dropped  from  a  very  high  tower  falls 
exactly  on  the  spot  right  below  ;  or  how  cannon-balls  fired 
from  a  large  culverin  with  equal  charges  of  gunpowder  of  the 
same  quality,  and  with  the  gun  pointed  at  the  same  angle  with 
the  horizon,  have  exactly  the  same  range  to  eastward  and  to 
westward,  the  earth  moving  to  the  east.  But  they  who  urge 
such  arguments  are  mistaken  through  not  understanding  the 
nature  of  primary  globes  and  the  combination  of  parts  with 
their  globes,  albeit  not  conjoined  thereto  with  bonds  of  solid 
matter.  But  the  earth  in  its  diurnal  revolution  does  not  so 
move  that  its  more  solid  circumference  is  separated  from  the 
bodies  circumfused ;  on  the  contrary,  all  the  circumfused  efflu- 
ences, and  all  heavy  bodies  therein,  howsoever  shot  thereinto, 
advance  simultaneously  and  uniformly  with  the  earth  because 
of  the  general  coherence.  This  is  the  case  in  all  primary 
bodies, — the  sun,  moon,  earth, — the  parts  betaking  themselves 
to  their  origin  and  founts,  whereunto  they  are  attached  with 
the  same  appetence  with  which  what  we  call  heavy  bodies  are 
attached  to  earth.  Thus  lunar  bodies  tend  to  the  moon,  solar 
to  the  sun,  within  the  respective  spheres  of  their  effluences. 
These  effluences  cohere  through  continuity  of  substance ;  and 
heavy  bodies,  too,  are  united  to  earth  by  their  heaviness  and 
advance  with  it  in  the  general  movement,  especially  when  no 
resistance  of  bodies  hinders.  And,  for  this  reason,  the  diurnal 
revolution  of  the  earth  does  not  sweep  bodies  along  nor  retard 


ARGUMENT  AGAINST  EARTH'S  MOTION— REFUTATION.  34I 

them  :  they  neither  outstrip  the  earth's  motion  nor  fall  behind 
when  shot  with  force,  whether  to  east  or  to  west.     Let  EFG 


be  the  earth,  A  the  centre,  LE  the  ascending  effluences.  As 
the  sphere  of  the  effluences  moves  with  the  earth,  so  the  part 
of  the  sphere  on  the  right  line  LE  proceeds  undisturbed  in  the 
general  rotation.  In  LE  the  heavy  body  M  falls  perpendicu- 
larly to  E,  the  shortest  route  centreward ;  nor  is  this  right 
motion  oi  M  a  composite  motion,  i.e.,  resultant  of  a  motion 
of  coacervation  and  a  circular  motion,  but  simple  and  direct, 
never  going  out  of  the  line  LE.  And  an  object  shot  with 
equal  force  from  E  toward  F,  and  from  E  toward  G,  has  the 
same  range  in  both  directions,  though  the  diurnal  rotation  of 
the  earth  goes  on  ; — even  as  twenty  steps  taken  by  one  man 
cover  the  same  distance  eastward  as  westward.  Hence  the 
diurnal  revolution  of  the  earth  is  not  at  all  refuted  by  the  illus- 
trious Tycho  Brahe  through  such  arguments  as  these. 

The  tendence  to  its  centre  (called  by  philosophers,  weight) 


342 


WILLIAM  GILBERT. 


works  no  resistance  to  the  diurnal  revolution,  neither  does  it 
give  direction  to  the  earth,  nor  keep  in  place  the  parts  of  the 
earth,  which  have  no  weight  when  resting  in  the  earth's  solid 
substance  :  there  they  have  no  longer  any  tendence,  but  are  at 
rest  in  its  mass.  If  there  be  a  flaw  in  the  mass,  a  cavity  of 
looo  fathoms  for  example,  a  homogenic  part  of  the  earth  or 
compacted  terrestrial  matter  descends  through  that  space,  be 
it  filled  with  water  or  with  air,  to  a  more  definite  centre  {prin- 
cipium)  than  air  or  water,  and  seeks  the  solid  globe.  But  the 
centre  of  the  earth,  as  also  the  whole  earth  itself,  has  no  weight: 
separated  parts  tend  to  their  principium,  and  this  tendence  we 
call  weight :  parts  in  union  are  at  rest,  and  even  if  they  had 
weight,  they  would  cause  no  impediment  to  the  diurnal  revo- 
lution.    For  if  around  the  axis  AB  a  weight  be  at  C,  it  is 


balanced  by  E',  at  F  it  is  balanced  by  G^ ;  if  at  Ify  by  /.  And, 
similarly,  if  it  is  at  L,  it  is  balanced  by  M.  Thus  the  whole 
globe,  having  a  natural  axis,  is  balanced  in  equilibrium  and  is 
set  in  motion  easily  by  the  slightest  cause,  but  chiefly  for  the 
reason  that  the  earth,  in  its  own  place,  is  in  no  wise  heavy  nor 


DEFINITE  TIME  OF   THE  REVOLUTION  OF   THE  EARTH.   343 

needs  any  balancing.  Hence  no  weight  hinders  the  diurnal 
revolution,  and  no  weight  gives  to  the  earth  direction  or  con- 
tinuance in  its  place.  It  is  therefore  plain  that  no  argument  of 
sufificient  force  has  yet  been  formed  by  philosophers  to  refute 
the  earth's  motion. 


CHAPTER  VI. 

OF  THE  CAUSE  OF  THE  DEFINITE  TIME  OF  THE  TOTAL 
REVOLUTION  OF  THE  EARTH. 

The  causes  of  the  diurnal  motion  are  to  be  found  in  the 
magnetic  energy  and  in  the  alliance  of  bodies :  that  is  to  say, 
why  a  revolution  of  the  earth  is  performed  in  the  term  of  24 
hours.  For  no  ingenious  artifice,  whether  of  clepsydra,'  or  of 
hour-glasses,  or  of  time-pieces  with  toothed  wheels  and  driven 
by  the  tension  of  a  steel  plate,  can  show  any  difference  of  time. 
But  the  diurnal  revolution  once  accomplished  comes  on  again. 
Now  we  will  take  a  day  to  mean  a  complete  revolution  of  a 
meridian  of  the  earth  from  sun  to  sun.  This  is  a  little  less 
than  the  total  revolution ;  for  in  365I-  turnings  of  a  meridian 
to  the  sun  a  year  is  completed.     Because  of  this  fixed  and 

'  The  Clepsydra,  or  water  clock,  is  said  by  Vitruvius  to  have  been  first 
made  by  the  Egyptians  or  Persians.  Perhaps  the  most  remarkable  one  was 
that  sent  as  a  present  by  Haroun,  grandson  of  Almansor,  to  Charlemagne  in 
A.D.  799.  In  the  dial-plate  were  12  doors,  equally  distant,  upon  which  were 
inscribed  the  hours  successively  ;  each  door  opened  in  its  turn,  and  let  fall, 
upon  a  brazen  bell,  a  sufficient  number  of  balls  to  strike  the  proper  hour.  The 
doors  continued  open  till  12  o'clock,  when  12  little  knights,  mounted  on  horse- 
back, issued  simultaneously  from  a  part  of  the  machine,  paraded  around  the 
dial,  and,  having  closed  the  12  doors,  as  suddenly  retired  (Morel,  "  Elem. 
Ph.  and  Sc,"  London  1827,  pars.  210,  224.  Consult  M.  Delambre,  "Hist,  de 
I'Astr.  Anc  ,"  Paris  1817,  Vol.  I,  Table  page  Ivii). 


344  WILLIAM  GILBERT. 

constant  motion  of  the  earth  the  number  and  time  of  365  days 
5  hours  55  minutes  are  always  fixed  and  settled,  barring  that 
for  other  causes  there  are  certain  trifling  differences.  Thus 
the  earth  revolves,  not  fortuitously  nor  by  chance,  nor  with  a 
headlong  motion,  but  evenly,  with  a  certain  high  intelligence 
and  with  a  wonderful  steadiness,  even  like  the  rest  of  the 
movable  stars  which  have  fixed  periods  for  their  movements. 

Thus,  inasmuch  as  the  sun  itself  is  the  mover  and  inciter 
of  the  universe,  the  other  planets  that  are  situate  within  the 
sphere  of  his  forces,  being  impelled  and  set  in  motion,  do  also 
with  their  own  forces  determine  their  own  courses  and  revolve 
in  their  own  periods,  according  to  the  amplitude  of  their  greater 
rotation  and  the  differences  of  the  forces  effused  and  the  per- 
ception of  a  greater  good.  Hence  it  is  that  Saturn,  having  a 
greater  course  to  run,  revolves  in  a  longer  time,  while  Venus 
revolves  in  nine  months,  and  Mercury  in  80  days,  according  to 
Copernicus ;  and  the  moon  makes  the  circuit  of  the  earth  in 
29  days  12  hours  44  minutes.  We  have  asserted  that  the 
earth  turns  on  its  centre,  making  one  day  in  its  revolution  sun- 
ward. The  moon  goes  round  the  earth  in  a  monthly  course, 
and  when  after  its  prior  conjunction  with  the  sun  it  comes  to 
conjunction  again,  it  constitutes  one  month,  or  one  lunar  day. 
The  mean  distance  of  the  moon's  orbit,  according  to  the  calcu- 
lations of  Copernicus  and  other  later  astronomers,  is  distant 
from  the  earth's  centre  about  29I-  diameters  of  the  earth.  A 
solar  revolution  of  the  moon  in  her  orbit  takes  29  days  12 
hours  44  minutes.  We  reckon  her  periodic  time  by  her  re- 
turn to  the  same  position  relatively  to  the  sun,  making  the 
moon's  solar  revolution,  not  by  her  return  to  the  same  absolute 
position,  making  the  complete  or  stellar  revolution,  just  as  one 
day  on  earth  is  reckoned  as  the  planets  return  to  the  same 
position  relatively  to  the  sun,  and  not  absolutely ;  because  the 


DEFINITE  TIME  OF   THE  REVOLUTION  OF   THE  EARTH.  345 

sun  is  the  cause  of  both  the  earth's  and  the  moon's  motions. 
Also,  because  (as  more  recent  astronomers  suppose)  the  month, 
as  measured  between  solar  conjunctions,  is  really  the  full  period 
of  revolution,  because  of  the  earth's  motion  in  her  great  orbit. 
Diameters  bear  a  constant  ratio  to  circumferences.  And  the 
moon's  orbit  is  a  little  more  than  twice  29I  times  the  length 
of  great  circles  on  the  earth. 

Thus  the  moon  and  the  earth  agree  in  a  twofold  ratio  of 
motion,  and  the  earth  rotates  in  its  diurnal  motion  in  the 
space  of  24  hours ;  because  the  moon  has  a  motion  propor- 
tioned to  the  earth,  and  the  earth  has  a  motion  agreeing  in  a 
twofold  proportion  with  the  moon's  motion.  There  is  some 
difference  in  minutes,  for  the  distances  of  the  stars  are  not 
sufficiently  determined  in  minutes,  nor  are  astronomers  agreed 
thereupon.  So,  then,  the  earth  rotates  in  the  space  of  24 
hours,  even  as  the  moon  does  in  her  monthly  course,  by  a 
magnetical  compact  of  both,  the  globes  being  impelled  for- 
ward according  to  the  ratio  of  their  orbits,  as  Aristotle  admits 
{de  Ccelo,  Book  II,  Chap.  X).  '*  It  comes  about,"  says  he,  "  that 
the  motions  of  each  are  performed  in  a  ratio,  to  wit,  in  the 
same  intervals  whereby  some  are  quicker,  others  slower."  But 
as  between  the  moon  and  the  earth,  it  is  more  reasonable  to 
beheve  that  they  are  in  agreement,  because,  being  neighbor 
bodies,  they  are  very  like  in  nature  and  substance,  and  be- 
cause the  moon  has  a  more  manifest  effect  on  the  earth  than 
have  any  of  the  other  stars,  except  the  sun ;  also  the  moon 
alone  of  all  planets  directs  its  movements  as  a  whole  toward 
the  earth's  centre,  and  is  near  of  kin  to  earth,  and  as  it  were 
held  by  ties  to  earth. 

Such,  then,  is  the  symmetry  and  harmony  of  the  moon's 
and  the  earth's  movements,  very  different  from  the  oft-men- 
tioned harmony  of  the  celestial  motions,  which  requires  that 


34^  WILLIAM  GILBERT. 

the  nearer  any  sphere  is  to  the  primum  mobile  and  to  the 
imaginary  and  fictitious  rapid  first  motion,  the  less  it  opposes 
it  {contranitatur)  and  the  more  slowly  it  is  borne  by  its  own 
motion  from  west  to  east ;  but  that  the  farther  it  is  away  the 
more  rapidly  and  the  more  freely  it  performs  its  motion,  and 
hence  that  the  moon  (being  farthest  from  the  primum  mobile) 
revolves  with  greatest  rapidity.  These  absurdities  have  been 
accepted  for  the  sake  of  the  primum,  'mobile,  and  so  that  it 
might  seem  to  have  some  effect  in  retarding  the  movements 
of  the  nether  heavens ;  as  though  the  motion  of  the  stars  was 
due  to  retardation,  and  was  not  inborn  and  natural  to  them, 
and  as  though  the  rest  of  the  heavens  (the  primum  -mobile 
alone  excepted)  were  ever  driven  by  a  mighty  force  with  a 
mad  impulsion.  Far  more  probable  is  it  that  the  stars  revolve 
symmetrically,  with  a  certain  mutual  concert  and  harmony.* 

'  Dr.  Wm.  Whewell  says  ("  Hist,  of  the  Ind.  Sc,"  1859,  Vol.  I,  page 
394)  that  Gilbert  had  only  some  vague  notions  that  the  magnetic  virtue  of  the 
earth  in  some  way  determines  the  direction  of  the  earth's  axis,  the  rate  of  its 
diurnal  rotation,  and  that  of  the  revolution  of  the  moon  about  it.  He  died  in 
1603,  and  in  his  posthumous  work  {De  Mundo  nostra  Sublunari  Philosophia 
nova,  1631)  we  have  already  a  more  distinct  statement  of  the  attraction  of  one 
body  by  another.  "  The  force  which  emanates  from  the  moon  reaches  to  the 
earth,  and,  in  like  manner,  the  magnetic  virtue  of  the  earth  pervades  the  region 
of  the  moon :  both  correspond  and  conspire  by  the  joint  action  of  both,  accord- 
ing to  a  proportion  and  conformity  of  motions,  but  the  earth  has  more  effect  in 
consequence  of  its  superior  mass  ;  the  earth  attracts  and  repels  the  moon,  and 
the  moon,  within  certain  limits,  the  earth  ;  not  so  as  to  make  the  bodies  come 
together,  as  magnetic  bodies  do,  but  so  that  they  may  go  on  in  a  continuous 
course."  Though  this  phraseology  is  capable  of  representing  a  good  deal  of 
the  truth,  it  does  not  appear  to  have  been  connected,  in  the  author's  mind, 
with  any  very  definite  notions  of  mechanical  action  in  detail. 


THE  EARTH'S  PRIMARY  MAGNETIC  NATURE.        347 


CHAPTER  VII. 

OF  THE  earth's  PRIMARY  MAGNETIC  NATURE,  WHEREBY 
HER  POLES  ARE  MADE  DIFFERENT  FROM  THE  POLES  OF 
THE   ECLIPTIC. 

Having  shown  the  nature  and  causes  of  the  earth's  diurnal 
revolution,  produced  partly  by  the  energy  of  the  magnetic 
property  and  partly  by  the  superiority  of  the  sun  and  his  light, 
we  have  now  to  treat  of  the  distance  of  the  earth's  poles  from 
those  of  the  ecliptic — a  condition  very  necessary  for  man's 
welfare.  For  if  the  poles  of  the  world  or  the  earth  were 
fixed  at  the  poles  of  the  zodiac,  then  the  equator  would  lie 
exactly  under  the  line  of  the  ecliptic,  and  there  would  be  no 
change  of  seasons, — neither  winter,  nor  summer,  nor  spring, 
nor  fall, — but  the  face  of  things  would  persist  forever  unchang- 
ing. Hence  (for  the  everlasting  good  of  man)  the  earth's  axis 
declined  from  the  pole  of  the  zodiac  just  enough  to  suffice  for 
generation  and  diversification.  Thus  the  declination  of  the 
tropics  and  the  inclinations  of  the  earth's  pole  always  stand 
in  the  24th  degree,  but  is  at  present  only  23  deg.  28  min.,  or, 
according  to  others,  29  minutes ;  but  formerly  the  declination 
was  23  deg.  52  min.,  and  that  is  the  uttermost  limit  of  declina- 
tion so  far  observed.  This  has  been  wisely  ordered  by  nature 
and  settled  by  the  earth's  primary  eminency.  For  were  those 
poles — those  of  the  earth  and  the  ecliptic — to  be  much  farther 
apart,  then  as  the  sun  approached  the  tropic  all  things  would 
be  waste  and  ruin,  in  any  high  latitude  of  the  other  and 
neglected  portion   of  the  globe,  because   of  the  protracted 


348  WILLIAM  GILBERT. 

absence  of  the  sun.  But  now  all  things  are  so  disposed  that 
the  entire  globe  of  earth  has  its  own  changes  in  due  succession, 
its  own  fitting  and  needful  seasons,  either  through  a  more 
direct  radiation  from  overhead  or  by  a  longer  tarrying  of  the 
sun  above  the  horizon. 

Around  these  poles  of  the  ecliptic  the  bearing  of  the 
earth's  poles  rotates,  and  because  of  this  motion  we  have  the 
precession  of  the  equinoxes. 


CHAPTER  VIII. 

OF  THE  PRECESSION  OF  THE  EQUINOXES  BY  REASON  OF 
THE  MAGNETIC  MOVEMENT  OF  THE  EARTH'S  POLES  IN 
THE  ARCTIC  AND  ANTARCTIC  CIRCLE  OF  THE  ZODIAC. 

The  early  astronomers,  not  noting  the  inequality  of  years, 
made  no  distinction  between  the  equinoctial  or  solstitial  re- 
volving year  and  the  year  determined  from  a  fixed  star.  They 
also  deemed  the  Olympian  years,  which  were  reckoned  from 
the  rising  of  the  Dog  Star  or  Sirius  {Caniculd)  to  be  the  same 
as  those  reckoned  from  the  solstice.  Hipparchus  the  Rhodian 
was  the  first  to  notice  that  there  is  a  difference  between  the 
two,  and  found  another  year,  calculated  from  fixed  stars,  of 
greater  length  than  the  equinoctial  or  solstitial :  hence  he  sup- 
posed that  the  stars  too  have  a  consequent  motion,  though  a 
very  slow  one,  nor  readily  noticeable.  After  Hipparchus, 
Menelaus,  a  Roman  geometer,  then  Ptolemy,  and,  a  long  time 
afterward,  Machometes  Aracensis  and  several  others,  in  all 
their  writings  have  held  that  the  fixed  stars  and  the  whole  fir- 


THE  PRECESSION  OF   THE  EQUINOXES.  349 

mament  have  a  consequent  forward  movement  {in  consequentia 
procedere),  for  they  contemplated  the  heavens  and  not  the  earth, 
and  knew  nothing  of  the  magnetic  incHnation.  But  we  will 
prove  that  this  motion  proceeds  from  a  certain  revolution  of 
the  earth's  axis,  and  that  the  eighth  sphere,  so  called,  the  fir- 
mament, or  aplanes,  with  its  ornament  of  innumerable  globes 
and  stars  (the  distances  of  which  from  earth  have  never  been 
by  any  man  demonstrated,  nor  ever  can  be),  does  not  revolve. 
And  surely  it  must  seem  more  probable  that  the  appearances 
of  the  heavens  should  be  produced  by  a  deflection  and  inclina- 
tion of  the  small  body,  the  earth,  than  by  a  whirling  of  the 
whole  system  of  the  universe — especially  as  this  movement  is 
ordered  for  the  good  of  the  earth  alone,  and  is  of  no  benefit  at 
all  to  the  fixed  stars  or  the  planets.  For  by  this  motion  the 
rising  and  setting  of  stars  in  all  horizons  are  changed,  as  also 
their  culminations  in  the  zenith,  so  that  stars  that  once  were 
vertical  are  now  some  degrees  distant  from  the  zenith.  Pro- 
vision has  been  made  by  nature  for  the  earth's  soul  or  its 
magnetic  energy — just  as  in  attempering,  receiving,  and  divert- 
ing the  sun's  rays  and  light  in  fitting  seasons,  it  was  necessary 
that  the  bearings  of  the  earth's  pole  should  be  23  degrees  and 
more  distant  from  the  poles  of  the  ecliptic ;  so  that  now  in 
regulating  and  in  receiving  in  due  order  and  succession  the  lu- 
minous rays  of  the  fixed  stars,  the  earth's  poles  should  revolve 
at  the  same  distance  from  the  ecliptic  in  the  arctic  circle  of 
the  ecliptic,  or  rather  that  they  should  creep  with  slow  gait, 
because  the  actions  of  the  stars  do  not  always  persist  in  the 
same  parallel  circles,  but  have  a  slower  change ;  for  the  influ- 
ences of  the  stars  are  not  so  powerful  that  the  desired  course 
should  be  more  rapid.  So  the  axis  is  inflected  slowly,  and  the 
rays  of  the  stars  are  changed  in  such  length  of  time  as  the  di- 
ameter of  the  arctic  or  polar  circle  extends ;  hence  the  star  in 


3 so  WILLIAM   GILBERT. 

the  extremity  of  the  tail  of  Cynosura,  which  once  (i.e.,  in  the 
time  of  Hipparchus)  was  12  degrees  24  minutes  distant  from 
the  pole  of  the  world  or  from  the  point  which  the  earth's  pole 
regarded,  now  is  distant  from  it  only  2  degrees  52  minutes ; 
hence  from  its  nearness  to  the  pole  it  is  called  by  the  moderns 
the  Pole  Star.'  It  will  not  be  only  \  degree  from  the  pole,  but 
thereafter  will  begin  to  recede  till  it  reaches  a  distance  of  48 
degrees ;  that,  according  to  the  Prutenic  tables,''  will  be  A.D. 
15,000.  So  the  bright  star  (which  for  us  here,  in  southern 
Britain,  now  almost  culminates)  will  in  time  come  within  five 
degrees  of  the  world's  pole.  Thus  do  all  the  stars  change 
their  light  rays  at  the  earth's  surface,  because  of  this  admirable 
magnetic  inflection  of  the  earth's  axis.  Hence  the  ever  new 
changes  of  the  seasons  ;  hence  are  regions  more  or  less  fruitful, 
more  or  less  sterile ;  hence  changes  in  the  character  and  the 
manners  of  nations,  in  governments  and  in  laws,  according  to 
the  power  of  the  fixed  stars,  the  strength  thence  derived  or 
lost,  and  according  to  the  individual  and  specific  nature  of  the 
fixed  stars  as  they  culminate ;  or  the  effects  may  be  due  to 


1  Hakewill  alludes  {Apologie,  1635,  Lib.  ii,  page  97)  to  Hipparchus, 
"who  reports  that  in  his  time  the  starre  commonly  called  the  Polar  Starre, 
which  is  in  the  tayle  of  the  lesser  Beare,  was  12  degrees  and  two-fifths  distant 
from  the  Pole  of  the  ^Equator.  This  starre,  from  age  to  age,  hath  insensibly 
still  crept  nearer  to  the  Pole,  so  that  at  this  present  it  is  not  past  three  de- 
grees distant  from  the  Pole  of  the  Equator.  When  this  starre  then  shall  come 
to  touch  the  Pole,  there  being  no  farther  place  left  for  it  to  go  forward  (which 
may  well  enough  come  to  pass  with  five  or  six  hundred  yeares)  it  is  likely  that 
then  there  shall  be  a  great  change  of  things,  and  that  this  time  is  the  period 
which  God  hath  prefixed  to  Nature."  (See  Morell's  "Elem. . .  .Phil,  and  Sc," 
London  1827,  pp.  116-119^^^1?^.) 

*  The  Prutenic  (Prussian)  Astronomical  Tables, — PruteniccB  Tabula  Cceles' 
Hum  Motuum,  1551,  1571,  1585, — based  upon  the  observations  of  Copernicus, 
Hipparchus,  and  Ptolemy,  were  the  result  of  seven  years'  labor  on  part 
of  the  German  astronomer  Erasmus  Reinhold,  who  named  the  work  after  his 
benefactor,  Albert,  Duke  of  Prussia, 


THE  PRECESSION  OF   THE  EQUINOXES.  351 

their  risings  and  settings  or  to  new  conjunctions  in  the  me- 
ridian. 

The  precession  of  the  equinoxes  from  the  equal  motion  of 
the  earth's  pole  in  the   zodiacal  circle  is  here  demonstrated. 


Let  ABCD  be  the  ecliptic ;  lEG  the  Arctic  zodiacal  circle. 
Now  if  the  earth's  pole  looks  toward  E,  then  the  equinoxes 
are  at  D,  C.     Suppose  this  to  be  in  the  time  of  Metho/  when 

'  The  celebrated  astronomer  Meton  flourished  at  Athens  B.C.  432-430. 
The  mean  length  of  the  Metonic  Cycle,  or  Metonic  Year,  was  6939I  days, 
which  coincides  with  19  Julian  Years  and  nearly  corresponds  to  235  lunations. 
An  improvement  on  the  Metonic  Cycle  was  proposed  by  Calippus  of  Cyzicus, 
a  disciple  of  Plato,  The  Calippic  Period  consisted  of  76  years,  representing 
four  Metonic  Cycles,  or  about  940  complete  lunations,  1020  nodal  and  1016 
complete  sidereal  revolutions.  After  this,  says  Hakewill,  {Apologie  1635,  Lib. 
Ill,  page  279),  Hipparchus  framed  another  Cycle, "  containing  foure  of  Calippus 
his  periods,  each  of  them  (all  in  turn)  finding  some  errour  in  the  former  obser- 


352  WILLIAM  GILBERT. 

the  horns  of  Aries  were  in  the  equinoctial  colure.*  But  if  the 
earth's  pole  has  advanced  to  /,  then  K^  L  will  be  the  equinoxes, 
and  stars  in  the  ecliptic  C  will  seem  to  have  moved  forward 
over  the  whole  arc  KC,  following  the  signs;  L  advances  by- 
precession  over  the  arc  DL,  counter  to  the  order  of  the  signs ; 
but  the  opposite  would  be  the  case  if  the  point  G  were  to 
regard  the  earth's  poles,  and  the  motion  be  from  E  toward  G ; 
for  then  M,  iV  would  be  the  equinoxes,  and  the  fixed  stars  would 
anticipate  at  C  and  D,  counter  to  the  order  of  the  signs. 


CHAPTER   IX. 

OF  THE  ANOMALY  OF  THE    PRECESSION  OF    THE    EQUINOXES 
AND   OF  THE   OBLIQUITY  OF  THE  ZODIAC. 

The  change  in  the  equinoxes  is  not  always  equal,  but 
becomes  sometimes  more  rapid,  sometimes  more  slow ;  for  the 
earth's  poles  travel  unequally  in  the  Arctic  and  in  the  Antarc- 
tic zodiacal  circle,  and  recede  from  the  middle  line  on  both 

vations  which  they  diligently  amended. ..."  Hipparchus,  first  and  greatest  of 
Greek  astronomers,  is  the  inventor  of  the  astrolabe  as  well  as  the  discoverer  of 
the  "precession  of  the  equinoxes,"  and  left  many  important  works  including  a 
catalogue  showing  the  latitude  and  longitude  of  over  looo  stars.  It  was  Coper- 
nicus, however,  who  first  gave  the  true  explanation  of  the  phenomenon  known 
as  the  precession  of  the  equinoxes,  and  Newton  who  discovered  its  physical  cause 
(G.  J.  Chambers,  "  Descrip.  Astronomy,"  Oxford  1867,  page  240). 

'  The  colure  is  one  of  two  great  circles  which  intersect  at  right  angles  in 
the  poles  of  the  equator.  To  Eratosthenes,  the  Librarian  at  Alexandria,  who 
flourished  about  A.C.  280,  is  attributed  the  invention  and  construction  of  an  in- 
genious and  useful  instrument  or  machine,  having  some  resemblance  to  the 
armillary  sphere,  which  exhibited  the  relations  of  the  meridian  to  the 
equatorial  and  ecliptic  lines,  and  thus  indicated  the  solstitial  and  equinoctial 
colures. 


ANOMALY  OF   THE  PRECESSION  OF   THE  EQUINOXES.  353 

sides ;  hence  the  obliquity  of  the  zodiac  seems  to  change  to 
the  equator  {ad  cBquatorem  immutari).  And  when  this  became 
known  through  protracted  observations,  it  was  apparent  that 
the  true  equinoctial  points  were  elongated  from  the  mean 
equinoctial  points  70  minutes  to  one  side  or  the  other  in 
the  gr&dit&st  prostaphceresi ;  while  the  solstices  either  approach 
the  equator  equally  by  12  minutes  or  recede  to  the  same 
extent ;  so  that  the  nearest  approach  is  23  deg.  28  min. 
and  the  greatest  elongation  23  deg.  52  min.  Astron- 
omers in  accounting  for  this  inequality  of  precession  and 
of  declination  of  the  tropics  have  offered  "various  theories. 
Thebitius,  to  estabHsh  a  law  for  these  great  inequalities  in  the 
movements  of  the  stars,  held  that  the  eighth  sphere  does  not 
advance  by  continued  motion  from  west  to  east,  but  that  it  has 
a  sort  of  tremulous  motion  {inotu  quodam  trepidationis  concuti) 
whereby  the  leading  stars  in  Aries  and  in  Libra  of  the  eighth 
heavens  describe  around  the  leading  stars  of  Aries  and  Libra 
of  the  ninth  sphere  certain  small  circles  with  diameters  equal 
to  about  nine  degrees.  But  as  this  **  motion  of  trepidation"  ' 
is  full  of  absurdities  and  impossible  motions,  this  movement 
has  gone  out  of  fashion.  Other  astronomers,  therefore,  are 
compelled  to  ascribe  motion  to  the  eighth  sphere,  and  atop  of 
this  to  construct  a  ninth  heaven,  nay  a  tenth  and  an  eleventh.^ 
We  must  pardon  slips  in  mathematicians,  for  one  may  be  per- 
mitted in  the  case  of  movements  difficult  to  account  for  to  offer 
any  hypotheses  whatever  in  order  to  establish  a  law  and  to 
bring  in  a  rule  that  will  make  the  facts  agree.  But  the  phil- 
osopher never  can  admit  such  enormous  and  monstrous  celes- 
tial constructions. 


'  See  note,  Book  III,  Chap.  I. 
«  See  note.  Book  VI,  Chap.  III. 


354  WILLIAM  GILBERT. 

Now  though  we  see  in  all  this  how  loath  these  mathema- 
ticians are  to  ascribe  any  motion  to  the  earth,  which  is  a  very 
small  body,  nevertheless  they  drive  and  whirl  the  heavens, 
which  are  vast  and  immense  beyond  human  comprehension  and 
human  imagination :  they  construct  three  heavens,  postulate 
three  inconceivable  monstrosities,  to  account  for  a  few  unex- 
plained motions.  Ptolemy,  comparing  with  his  own  observa- 
tions those  of  Timochares  and  Hipparchus,  of  whom  the  one 
lived  260  years  before  his  day  and  the  other  460  years,  deemed 
this  to  be  the  motion  of  the  eighth  sphere  and  of  the  whole 
firmament,  and  proved  it  with  many  phenomena  on  the  poles 
of  the  zodiac  ;  and,  still  thinking  its  motion  to  be  equal,  he 
held  that  the  fixed  stars  in  100  years  travel  only  one  degree 
beneath  the  primum  mobile.  Seven  hundred  and  fifty  years 
after  him,  Abitegnius  found  that  one  degree  is  travelled  over 
in  66  years,  so  that  the  whole  period  would  be  23,760  years. 
Alphonsus  would  have  this  motion  still  slower — i  degree  28 
minutes  in  200  years ;  and  thus  would  the  course  of  the  fixed 
stars  proceed,  but  unequally.  At  last  Copernicus,  through  his 
own  observations  and  those  of  Timochares,  Aristarchus  the 
Samian,  Menelaus,  Ptolemy,  Machometes  Aracensis  and  Al- 
phonsus, discovered  the  anomalies  of  the  motion  of  the  earth's 
axis  ;  though  I  have  no  doubt  that  other  anomalies  also  will 
appear  some  centuries  hence,  for  it  is  difficult,  save  in  periods 
of  many  ages,  to  note  so  slow  a  movement,  wherefore  we  still 
are  ignorant  of  the  mind  of  nature,  what  she  is  aiming  at 
through  this  inequality  of  motion.  Let  A  be  the  pole  of  the 
ecliptic,  BC  the  echptic,  D  the  equator ;  when  the  earth's  pole 
regards  the  point  M  near  the  arctic  circle  of  the  zodiac  let  the 
anomaly  of  the  precession  of  the  equinox  be  at  F,  but  when  it 
regards  iV,  let  the  anomaly  of   the  precession  be  at  E.     So 


ANOMALY  OF   THE  PRECESSION  OF   THE  EQUINOXES.  355 

long  as  it  regards  /  directly  there  is  observed  the  maximum 
obliquity  G  in  the  solstitial  colure  ;  but  while  it  regards  Z, 


then  there  is  minimum  obliquity  H  in  the  colure  of  the  sol- 
stices. 


356 


WILLIAM  GILBERT. 


Copernicus' s  intorta  corolla  in  the  arctic  zodiacal  circle* 

FGB  is  one  half  of  an  arctic  circle  described  around  the 
pole  of  the  zodiac  ;  ABC  is  the  colure  of  the  solstices  ;  A  the 
pole  of  the  zodiac  ;  DE  the  anomaly  of  longitude  140  minutes 
on  either  side,  with  twofold  terminus  {duplici  termind) ;  BC 
anomaly  of  obliquity,  24  minutes ;  B  the  greater  obliquity, 
23  degrees  52  minutes  ;  D  the  mean  obliquity,  23  degrees  40 
minutes  ;  C  the  minimum  obliquity,  23  degrees  28  minutes. 


True  movement  and  natural  axis  {or  poles)  of  the  earth  directed 
toward  the  arctic  circle  of  the  zodiac. 

Let  AI  be  part  of  the  arctic  circle  of  the  zodiac  in  which  is  per- 
formed one  period  of  the  obliquity.  From  A  to  £  is  the  period 
of  the  anomaly  or  variation  of  the  precession  of  the  equinoxes. 
AI\s  the  curved  line  described  by  the  earth's  pole  in  a  true  mo- 
tion made  up  of  three  motions,  i.e.,  of  the  motion  of  the  preces- 
sions, and  of  the  anomaly  of  the  precessions,  and  of  obliquity. 


ANOMALY  OF   THE  PRECESSION  OF    THE  EQUINOXES.  35/ 

The  period  of  the  precession  of  the  equinoxes  is  25,816  Egyptian 
years ;  the  period  of  the  obliquity  of  the  zodiac  is  3434  years 
and  a  little  more ;  the  period  of  the  anomaly  of  the  precession 
of  the  equinoxes  is  1717  years  and  a  little  more.  If  we  divide 
the  whole  time  of  the  motion  from  ^  to  /  into  eight  equal 
parts,  in  the  first  eighth  part  the  pole  travels  faster  from  A  to 


B  ;  in  the  second  more  slowly  from  B  to  C;  in  the  third,  with 
the  same  slowness  from  Cto  B;  in  the  fourth,  more  rapidly 
again  from  D  to  ^;  in  the  fifth,  with  equal  rapidity  from 
£  to  F;  again  more  slowly  from  Fto  G;  with  the  same  slow- 
ness from  G  to  H;  in  the  last  eighth  again  more  rapidly  from 
H  to  /,  and  this  is  Copernicus's  intorta  corolla  *  with  mean 
motion  fused  into  a  curved  line,  which  is  the  true  path  of  the 


'  See  Nicolai  Copernid  Torinensis,  De  Revolutionibus  orbium  calestium, 
Norimbergiae  1543,  pages  66,  67,  or  the  Amstelrodami  ed.  of  1617,  pages  154- 
157.  The  intorta  corolla  is  not  an  inverted  but  an  irregular  crown  :  a  figure 
representing  the  successive  positions  produced  by  the  projection  of  the  earth's 
pole  upon  the  stellar  sphere,  resembling  a  crown,  but  distorted  by  the  irregular- 
ities of  motion.  (Consult,  also,  Rheticus,  "  Narratio  prima  de  Lib.  Rev.  Co- 
pernici;"  Kepler,  "De  Temporis  aequatione  plenaria  et  motu  octavae  sphaerae.) 


358 


WILLIAM  GILBERT. 


motion.  And  so  the  pole  reaches  the  extreme  limit  of  varia- 
tion of  the  precession  of  the  equinoxes  twice,  but  the  limit  of 
inclination  or  obliquity  once  only.  Thus  do  the  moderns,  and 
in  particular  Copernicus,  restorer  of  astronomy,  describe  the 
variations  of  the  movement  of  the  earth's  axis,  so  far  as  the 
same  is  made  possible  by  the  observations  of  the  ancients  down 
to  our  day ;  but  we  still  lack  many  and  more  exact  observations 
to  fix  anything  positively  as  to  the  anomaly  of  the  movement 
of  the  precessions,  as  also  of  the  obliquity  of  the  zodiac.  For 
since  the  time  when  in  various  observations  this  anomaly  was 
first  noted,  only  one  half  of  a  period  of  obliquity  has  passed. 
Hence  all  these  points  touching  the  unequal  movement  of 
precession  and  obliquity  are  undecided  and  undefined,  and  so 
we  cannot  assign  with  certainty  any  natural  causes  for  the 
motion. 

Wherefore  we  here  bring  to  an  end  and  conclusion  our 
arguments  and  experiments  magnetical. 

FINIS. 


ffKACXMVS^ 


Siue 
PHYSIOLOGIAKaV^ 

DEMAGNETE, 

MA.GNETICISC?VE  CORPO^ 

RIBYS  ET  MAGtiO  MAGNATE 
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Guiliclttio  GilteHo  Colceftrctifi , 
Medico  LotulmcMfi'. 
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mis  paratrnmiiffacpaeritKeniis  exctcitlims'" 
ai/iltu^imedf  iradcamr  A  a^HaaAur . 

Omnia  nimc  cubocnlcr  rccpoHfla  da  emefl= 
daliia  quamatiietH  lucent  cdiicauda^  figns 


ris  illuf 


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FAC-SIMILE  TITLE  PAGE  OF  GILBERT'S    "  DE  MAGNETE,"   SECOND  EDITION,  1628. 

359 


^raBattiSyJive  Phyfiologia  Nova 

M  A  G  N  E  T  E  , 

Magneticifq;corporibus  &  magno 

Magnete  tellurc,  fcx  libris  comprehenfus^ 

aGulLlELMO     GlLBERTO   CoIcC- 

ftrenfi.  Medico  Londinenfi, 

In  quihus  ea,qua  adhanc  materiam jpt^ant  ^flurmii 

^  Argumen^is  isf  experimentis  exa^ifiime  abJoJutifi" 

me^  troBantur  iff  explkantur. 

Omnia  nunc  diligenter  recognita,&  emendatius quam  ante 
in  lucera  edita ,  auda  &  figuris  illu(|rata ,  opera  &  Audio  D . 

WOLFGANGI    LOCHMANS,   I.     U.    D, 

&  Machematici. 

Ad  calcem  libri  aMnBus  efl  Index  capltum ,  Rerum  Iff  Verhrum 
Iqcu^UtiJsimus,  qui  inpnore  tecHtione  defdetabatur. 


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FAC-SIMILE   TITLE   PAGE   OF   GILBERT'S    "  DE  MAGNETE,"   THIRD   EDITION. 


G  y  I  L  I  E  L  M  2      G  I  L  B  E  R.  T  I 
C_P_t_C  ESTRENS1$, 
Medici  Regii, 

De  Mundo  noftro  Sublunari 

PHILOSOPHIA 

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FAC-SIMILE  TITLE  PAGE  OF  GILBERT'S    "  DE  MUNDO   NOSTRO  SUBLUNARI  PHILO- 
SOPHIA  NOVA." 


GENERAL  INDEX. 


Abano    Pietro    di,     {Petrus   Aponus, 

1250-1316,)  2,  33 
Abitegnius,  354 

Abohali  (Hali  Abbas),  4,  13,  76 
Acies,  Aciarum,  32,  40,  55,  59 
Adamant  stone,  21 
Adamas,  21,  22,  2i8 
Affaitatus,  Fortunius,  4 
Afformed  iron,  112 
Agricola,  George,  3,   5,  20,  34,  45,  173, 

174 
Agrippa,  Cornelius,  4 
Agulhas,  Cape,  266 
Aimant,  21 

Airy,  G.  B.,  "Magnetism,"  284 
Albertus  Magnus,  4,  9,  13,  21,  33,    172 
Aldrovandi,  Ulysses,  215 
Alexander  of  Aphrodisias    (in  Caria), 

5,  78,  145 
Alfonso,  Diego,  266 
Allibone,  S.  A.,  "Critical  Diet,,"  xix 
Alphonsus — Alfonso    X.,    El    Sabio, 

321,  354 
Ambra,  76 

Ampelius,  Ansonio  L.,  4 
Amphitane,  172 
Anaxagoras,  gS,  308 
Anelectrics,  83 

Antiperisastis  (counteraction),  175 
Appian,  Peter,  8 
Apponensis,  Petrus,  4 
Aquinas,  Thomas,  5,  103 
Archelaus,  308 
Ardoniis,  Santes  de,  4 
Arias,  Montanus,  Benedictus,  (Benito 

Arias  Montano,  i527-i598,)7 
Arnaldus,  4 

Aristarchus  of  Sam  oth race,  317,  354 
Aristotle,  vi,  li,  2,  22,  32,  34,  35,  40, 

57.  63,  69,  72,  98,  105,  309,  312,  320, 

325,  335,  336,  337   345 


Arsinoe,  temple  of,  3  ' 

Asterisks     (throughout    the     present 

work),  xlix 
Attraction,  97 
Augustine,  St.,  {Aurelius  Augustinus, 

354-430,)  326 
Averroes,     (Ibn-Roshd,      1149-1198,) 

2,9 
Avicenna,  (Aben  Sina,  Ibn-Sina,  980- 

1037,)  4,  9.  45.  56,  58,  80 
Azuni,  Domenico  Alberto,  (1749-1827,) 

7 

Bacon,  Francis,  xii,  xiii,  xv,  xvi,  xxv 

Bacon,  Roger,  9 

Barbatus,  Hermolaus,  4 

Barlo  (Barlowe),  William,  xiii,  xiv,  xv, 

xxv,  xxvi,  14 
Benedictus,  Joannes  Baptista,  252 
Benjamin,   Dr.  Park,  v''  ^^''  ^^^ 
Bertelli  Barnabita,  9,  i^^,  167 
Bescherelle,  M.,  "  Gr^nd  Diet.,"  xx 
Bessard,  10,  179,  232 
Bianco,  Andrea,  252 
Biarmia,  12,  271 

"  Biographia  Britannica"  ix,  xxiii 
Blunderville,  Thomas,    "The   Theo- 

riques  .  .  .  ,"  xix 
Bodies,  electric  and  magnetic,  97 
"  Bone  of  Horus,"  17 
Boniface,  Saint,  (archbishop  of  Mainz, 

680-755,)  326 
Borough,  William,  14 
Boswell,  Sir  William,  xxv 
Bowen,  Mr,,  "  Comp.  Sys.  of  Geog,," 

XX 

Boyle,  Robert,  78,  92 
Bractece  (see  Scales  of  Iron) 
Brande,  W.  T.,  143 
Brando,  272 
Brasevolus,  Antonius  Musa,  4 

363 


3^4 


GENERAL  INDEX. 


Brayley  and  Britton's    "  Beauties  of 

England  and  Wales,"  ix 
Brewster,  Sir  David,  xv,  77 
Brietio,  Philip,  "  Paral.  Geog. ,"  xxi 
Brown,  Thos.,  {Fseudoloxia,)  xxvii,  2, 

4.  12,  53,  78,  107,  I43>  173,  215,  252, 

267,  303 
Brunet,  J.  C.  "Manuel,"  xix 

Cabeo,  Nic.  {Phil  Magn.),  xxvii,  g,  96, 

127,  13S,  167,  215,  246,  332 
Cabot,  Sebastian,  8 
Cselius  Calcaguinius,  14 
Calaber,  Hannibal  Roserius,  4 
Calamita,  21 

Calippus  of  Cyzicus,  351 
Can  dish — Cavendish,  Thomas,  xxxvii, 

181 
Carabe,  75 
Cardan,  214,  10,  32,  33,  45,  61,  69,  70, 

77,  80,  loi,  108,   145,  166,  170,  171, 

179,  232,  255 
Carnelian,  83 
Cassini,  J.  J.  D.,  240 
Cathochites,  172 
Cesare,  Giulio,  215 
Chalybes,  chalybs,  32,  37,  40,  43,  55 
Charleton,  Dr.  Walter,  xxvii 
Chinocrates,  3 

Church  of  San  Agostino  at  Rimini,  214 
Church  of  Saint  Jean  at  Aix,  215 
Church  of  the  Augustines  at  Mantua, 

215 

Clark,  Latimer,  F.R.S.,  vi 

Clarke,  Charles  L,,  xxi,  xxvii 

Clepsydra,  343 

Coition,  magnetic,  xxix,   74,  97,   105, 

129,  153,  155,  161,  200 
Coition,  sphere  of,  xxxii 
Columbus,  252 

Colures,  solstitial  and  equinoctial,  352 
Conactus  (mutual  action),  no,  in,  310 
Conformated  (iron  and  earth),  192 
Conformed,  114,  331 
Constable,  William,  F.  R.  S.,  xxvii 
Cooke,  Conrad  W. ,  xiii,  xx 
Copernicus,   Nicolaus,  315,  318,  321, 

344,  350,  352.  354,  356,  357,  35^ 
Cortesius,  232 
Corvo,  252 
Costa,  Josephus,  11 
Costa,  Philip,  214 
Costaeus,  Joannes,   5,   lOO,  338,   339, 

340 
Cotton,  Henry,   "Typog.  Gaz.,"  xx, 

xxi 
Creech,  Thomas,  100 
Crocus  Martis  {st&  "  Saffron  of  Mars"). 


Cur  tins,  57 

Cusanus,  Michael  (Cardinal),  2,  4, 104, 

168 
Cuspis,  xxviii 
Cynosura,  26,  129,  180,  331,  350 

Dante,  7 

Davis,  Henry,  73,  99 

Davy,  Dr.  John,  xv,  xxv,  75 

Declinatorium,  xxix 

Deformated,  210;  deformate,  309 

Descartes,  Ren6,  (i596-i650,)xv,  329, 

330 
Deschamps,  M.  "  Diet,  de  G6og,,"  xx, 

xxi 
Dias,  56 

Diego,  Alfonso,  266 
Digby,  Sir  Kenelm,  xv,  xviii,  24,  107, 

123,  138 
Dioscorides,  2,  17,  52 
Dip  or  inclination.  Book  V 
Directive  (vexsorial)  force,  called  ver- 

ticity,  183 
Dominicus  Maria  of  Ferrara,  315,  316 
Doria,  Andrea,  6 
Drake,  Francis,  xxxvii,  181 
Dryden,  John,  vii,  xxvii 

Ecphantus,  317 
Electric  attraction,  82,  83 
Electric  bodies,  83,  97 
Electric  emanation,  85 
Electric  force,  85 
Electric  motion,  97 
Electrical  effluvia,  78 
Electrical  movements,  85 
Electricity,  terrestrial,  97 
Electrics,  xxviii,  86,  95,  96,  176 
Electron,  75 
Emerelstone,  39 
Empedocles,  308 
Encelius,  5,  172 

English  Institute  of  Electrical  Engin- 
eers, xxi 
Epicurus,  98,  loi 
Equation  of  the  centre,  261 
Erastus,  Thomas,  5,  39 
Erastosthenes,  352 
Erckern,  Lazarus,  143 
Euace,  172 
Euriprides,  17,  21,  31 

Fallopius— Falloppio,  Gabriello,  (1513 

-1562,)  4,  56,  57,  174 
Fantis,  Antonius,  9,  166 
Faraday,  Michael,  xxii,  283 
Farrar,  John,  214 
Fernel,  J.  F.,  8 


GENERAL  INDEX, 


365 


Ferrarius  lapis,  16 

Ficinus,  Marcilius,  (1433-1499,)  6,  13, 

179 
Fjndlay,  A.  G.,  "  Class,  Atlas,"  xxi 
Fitzgerald,  Joseph,  v 
Flavius  Blondus,  6 
Form,  primary,  146,  149 
Forma,  vi,  85,  106 
Formate  soul,  311 
Fracastorio,    8,  9,  82,    109,    II4,    I15, 

144,  170,  176,  231. 
Frost,  Alfred  J.,  xx 
Fuller,  Dr.  Thomas,  ix,  xxiv,  xxvii 

Galen,  li,  3,  17,  52,   57,  63,  74,  80,  99, 

101,  102 
Galileo — Galilei  (1564-1642),  xii,  xiii, 

XV,  321 
Gama,  Vasco  da,  266 
Garcias  ab  Horto — Garcia  d'Orta,  53 
Gassendi,  xv,  215 
Gaudentius,  Merula,  13 
Geber,  36,  37,  38,  143 
Gehler,  J.  S.  T.,  18 
GelUbrand,  Henry,  240 
Gemma,  Cornelius,  loi 
Gilbert's    "  De  mundo  nostro,"   xxv, 

xxvii,  346 
Gilgil,  34 

Glanvil,  Barthol,  de,  2,  19 
Glanvill,  Jos.,  6 
Goia,  Joannes,  6 
Gold  magnet,  75 
Goropius,  7 
Graesse,  J.G.  T.,"Tr6sor  de  Livres," 

xix 
Graham,  George,  240 
Greely,  Com.  A.  W.,  230 
Grimaldi,  215 

Grotius,  Hugo,  xliv,  252,  254 
Gruter  John,  xxv 
Guyot  de  Provins,  7 

Hce7natites,   39 

Hakewill,  George,   45,  53,    320,    327, 

350,  35T 
Hakluyt,  Richard,  xxxviii 
Hall  Abbas  (Abohali),  4,  13,  76 
Hall,  Dr.  Isaac  H.,  vi 
Hallam,  Henry,  "  Intr.  to  Lit.,"  xii 
Harding,   S.  &  E.   "  Biogr.  Mirrour," 

xxiv 
Harlot,  Thomas,  14 
Harvey,  xv 
Heliodorus,  75 
Heraclea,  i6 

Heracleitus,  of  Ephesus,  308 
Heraclides  (Ponticus),  317 


Hermes,  309 

Hero  the  elder,  95 

Herschel,  F.  W.,  xi,  15 

Hipparchus   the  Rhodian — the  Bithy- 

nian,  315,  317,   348,    350,    351,  352, 

354 
Hippocrates  (b.c.  460-357),  li,  57,  82, 

99 
Hues,  Robert,  14 
Humboldt,    Alex.,    ("Cosmos,")  xiii, 

xvii,  xl,  7,  8,  9,  78,  97,  215,233,  234, 

2S3 
Humor  (unifier  of  all  things),  85,  92, 

96 
Hunt,  Arthur  Ackland,  xxiv 

Ibn-Roshd  (see  Averroes). 
Ibn-Sina  (see  Avicenna). 
Inclination  or  dip.  Book  V 
Informated    mine,  air   or  water,  185, 

305;  informed,  113 
Intorta    Corolla,  of   Copernicus,    356, 

357 

Johnson,  C.  F.,  99 

Kendall,  Abraham,  14,  266 

Kepler,  Johann,  (1571-1630,)  321,  357 

Kircheri,  h.X}a..,{Magnes  .  .  .  magnetica,) 

4.  138,  235 
Klaproth,  Julius  Heinrich  von,  (1783- 

1835,)  13 

Lactantius,  Lucius  Coelius,  326 

Lament,  Dr.  J.,  xx,  31,  137,  192 

Langius  Joannes.  4 

Larousse  M.,  "Grand  Diet.,"  xxi 

Lazos,  Roderigues  de,  266 

Leandro,  Francis,  45 

Leonhardus,  Camillus,  4 

Leslie,  Sir  John,  xix 

Levinus  Lemnius,  6 

Lewis,  Dr.  Charlton  T.,  vi 

Linea  Jiducialis,  263 

Linschooten,  Jan  Hugo  van,  xxxviii 

Livingston,  Dr.  Jos.  V.,  vi 

Livio  Sanuto,  11,  232,  252 

Loadstones,     armed     and     unarmed, 

xxviii,   137,  138,  139,  140 
Lochmann  —  Lochmans,      Wolfgang, 

xxi 
Long,  George,  "  Atlas,"  xxi 
Lovett,  R.,  ("Subtil  medium  provM  ",) 

330 
Lowndes,    W.   T.,    "  Bibl.    Manual," 

xix 
Lucas  Gauricus,  13 
Lucretius,  4,  5,  16,  81,  98,  99,  100 


366 


GENERAL  INDEX. 


Lully,  Raymond,  (1234-1315,)  7 
Lusitanus,  Amatus,  4 
Lyncurium,  75 
Lynschetensis,  Hugo,  xxxviii 

Machometis  Aracensis,  348,  354 

Maclean,  Alex.,  "Diet,  of  Am.Geog.," 
xxi 

MacMillan,  E.,  v 

Magnes,  21 

Magnesia,  16 

M agues s,   2i 

Magnetic  axis  and  poles,  128 

Magnetic  body,  excited,  xxxi 

Magnetic  bodies,  97 

Magnetic  coition  (see  Coition,  mag- 
netic). 

Magnetic  horizon,  128 

Magnetic  meridians,  126 

Magnetic  movements,  72 

Mahomet's  shrine,  3 

Manardus,  57 

Marbodaeas,  4,  14 

Marcellus,  4 

Marchasites,  marcasites,  37 

Maria,  Dominicus,  of  Ferrara,  315,  316 

Marsilius  of  Ficino,  232 

Martin,  T.  H.,  {Observ.  et  Thdories,)  4, 

13 

Martinus  Cortesius,  10,  179 

Materia,  vi,  85 

Matthiolus,  3,  4 

Mauritanus,  Serapio,  4 

Maurolycus,  Franciscus,  10,  68,  232, 
270 

Mayer,  Alfred  M.,  vi,  252 

Medicinal  power  of  the  iron,  55 

Medicinal  virtue  of  the  loadstone,  52 

Medina,  Pedro  de,  251 

Menelaus  —  Milieus,  Roman  geome- 
ter, 348,  354 

Menzies,  James,  li 

Metonic  Cycle,  351 

Microge,  or  terrella,  24 

Miller,  Geo.,  D.D.,  7 

Monro,  H.  A.  J.,  100 

Montagnana,  58 

Montanus,  Baptista,  4 

Morant,  Philip,  "  Hist,  of  Essex,"  ix, 
x,  xxiii 

"  Movement  of  trepidation,"  180,  353 

Munk,  "Roll  of  the  Coll.  of  Ph.  and 
Surgeons,"  xii,  xxiii 

Myseni,  40 

Newton,  Sir  Isaac,  (1642-1727,)  321, 
329,  352 


Nicander,  Colophonius,  15,  17 

Nicaulaus,  Myrepsus,  54 

Nicetas     Acominatus    or    Choniates, 

(1150-1216,)  317 
Niebuhr,  Barthold  Georg,  16 
Non-electrics,  83 
Nonius,  Petrus,  250 
Norman,  Robert,  xi,  10,  15,  232,  244 
Norumbeja,  234 
Nova  Zembla,  231,  269 

Offusius,  Jofrancus,  73 
Olaus  Magnus.  11,  12 
Orbis  virtutis,  xxii,  xxxi,  122,  1 50,  285 
Oribasius,  4 
Orpheus,  21,  98,  309 
Oviedo  y  Valdes,   Gonzalo  Fernandez 
de,  (1478-1557,)  8 

Pantarbes,  172 

Parocelsus,  5,  6,  54,  146 

Parmenides,  308 

Peirce,  Prof.  Charles  Sanders,  vi 

Peregrini,  Petri,  4,  9,  19,  166,  167,  179, 

232,  332 
Perpetual-motion  engine,  166 
Pettus,  Sir  J.,  143 
Philolaus,  of  Crotona,  318 
Philostratus,  Flavius,  of  Lemnos,  172 
Pictorius  (Quintus  Fabius  Pictor)  13, 

80 
Piedramant,  21 
Pieters,  Charles,  "Ann.  de  I'  Impr.," 

xxvii 
Plancius,  Peter,  xliii 
Plat,  Sir  Hugh,  2 
Platea,  56 
Plato,  2,  5,  17,  21,  31,  73,  98,  99,  241, 

308 
Pliny,  2,  3,   15,   17,  30,  32,43,  76,  77, 

170,  172,  173,  174,  316 
Plotinus  of  Alexandria  (204-274),  324 
Plutarch,  2,  54,  87,  99,  100 
Poggendorff,  J.  C,  xiii,  xix,  xxi 
Poles  of  the  earth,  xv,  9 
Polo,  Marco,  7,  11 
Porta,  J.  B.,  xxvii,  2,  11,  12,  17,  19,  32, 

37,  41,  102,  107,  108,  117,   144,  145, 

150,  158,  160,  173,  209,  217,  218,  219, 

226,  251 
Precession  of  the  equinoxes,  348,  352 
Priestley,  Dr.  Joseph,  xiii 
Primary  confluence,  98 
Primum  7nobile,  xiii,   126,  317,  320  et 

seq. ,  328,  336,  346,  354 
Prostaphceresis,  261 
Prutenic  (Prussian)  tables,  350 


GENERAL  INDEX. 


367 


Ptolemaeus,  CJaudius,  li,  2,  12,  17,  43, 
54,  142,  208,  315,  316,  317,  318,  321, 
323,  324,  340,  348,  350,  354 

Ptolemy  (Ptolemaeus  Philadelphus),  3 

Puteanus,  G.,  {Ratio  Furg.  Med.,)  5, 
loi,  102 

Pyrimachus,  40 

Pythagoras,  92,  308 

Quaritch,  Bernard,  xxvii 

Radius  (of  a  loadstone's  sphere),  xxix 
Radius,  radius  astronomicus,  256 
Razes — Rhazes,  57,  58 
Reaumur,  R.   A.   F.   de,  (1683-1757,) 

39 
Reinhold — Rheinhold, Erasmus,  (i 5 1 1- 
1553,)  316,  350 
*'  Respective  points  "  (Norman's),  xli, 

10,  244 
Revolution  of  the  Globes,  Book  VI 
Rheticus  —  George    Joachim,     (1514- 

1576,)  357 
Richardson,  Dr.  B.  W.,  xxiii,  li 
Riley,  Henry  T.,  xlv 
Robison,  Dr.  John,  xvi,  xix,  xxv 
Rohault,  J. — Rohaulti  Jacobi,  2,    79, 

138,  149,  215,  321 
Ross,  Sir  James  Clark,  282 
Ross,  Sir  John,  2S2,  283 
Rotary  needles,  use  of,  223 
Ruellius,  13 
Rueus,  Franciscus,  12 
Ruffinus  (Toranus),  3 

Saccheti,  F.,  56 

"  Saffron  of  Mars,"  56,  142,  143 

Sagda — Sagdo,  172 

Salmanasar,  33 

Salmasius,  76 

Sardonyx,  83 

Sarpi,  Fra  Paolo,  xv 

Scales  of  Iron  {bractecB),  39 

Scaliger, Julius  Caesar,  (1484-1558,)  10, 

61,  76,  103,  109,  113,  174,  232 
Scarella,    Giambattista,     "  De    Mag- 

nete,"  xviii 
Schmergel,  smeargel,  39 
Serapion,  12 
Serapis,  temple  of,  3 
Severtius,  Jacobus,  10 
Siderites,  16,  21,  22,  218 
Siegelstein,  21 
Silvaticus,  Matthaeus,  4 
Simon  {Clavis  Sanationis),  14 
Smiris,  39 
Smith,  Dr.  W.,  xxi,  16 


Solino,  C.  G.,  (Caius  Julius  Solinus,) 

Folyhistor,  2,  14,  17,  22,  172 
Solomon,  7,  8 
Sotacus,  17 

Sphere  of  coition,  xxix 
Sphere  of  influence,  xxix 
Stadius,  316 

Stevin,  Simon,  xliv,  252,  253,  254 
Stomoma,  40,  55,  59 
Succinum,  76 
Sudini — Sudavienses,  76 

Tacitus,  Cornelius,  43 

Taisner,  Joannes,  (Taisnier,)  g,  13,  19, 

166 
Terrella,  xviii,   xxii,  xxiv,  xxviii,  24, 

121,  124,  126,  150,  151,  210 
Terrestrial  electricity,  97 
Thabet  ben  Korrah,  180 
Thales,  xi,  22,  98,  109,  308,  312 
Theatnedes,  32 

Themistius,  "  Euphrades,"  114 
Theophrastus,  xi,  li,  2,  17,  21 
Thevenot,  166 
Thompson,    Silvanus    P.,    xx,   xxvi, 

xxvii,  283 
Thomson,  Thomas,  M.D.,  (1773-1852,) 

xiii,   22,   32,  36,   37,  39,  40,   76,  77, 

83,  143 
Thomson,    William,    (Lord     Kelvin,) 

xxii,  249,  283 
Timocaris — Timochares,  321,  354 
Topaz,  75 
Tourmaline,  75 
Transformated,  214 
Tycho  Brahe,  261,  321,  341 

Variation,  Book  IV 
Vasco  da  Gama,  266 
Versorium  magnetized,  xxviii 
Versorium       non-magnetized,      xviii, 

xxviii,  79,  81 
Vertices  (centres  of  whirling  motion), 

129 
Verticity,   xxviii,    48,    183,    189,    192, 

200,  208,  211,  217,  219,  223 
Vieta,  Francis,  xv 
Vigor  (primary  native  strength),  105 
Villanova,  Arnoldus  de,  14 
Vincentii  Burgundi,  (Vincent  de  Beau- 

vais),  4,  14,  21 
Virgilius,  bishop  of  Salzburg,  327 
Virgilius  {Vergilius),  Marco  P.,  37 
Vitruvius  Pollio,  Marcus,  316,  343 
Vitry,  Jacques  de,  7 

Wenckebach,  W,,  167 


368 


GENERAL  INDEX. 


Wetzler,  Joseph,  vi 

Whewell,  William,  xiii,  15,  74,  77,  78, 

105,  136,  240,  346 
Willems,  Alph.,  "  Les  Elzevier,"  xxvii 
Wood,  Anthony  A,  Athence  Oxionenses, 

ix,  xiv 
Wright,  Edward,  vi,  xxxvii,  xl,  14 


Wright,  Thomas,  "  Hist.  ...  of  Es- 
sex," ix,  xxxiii 

Zachary — Zacharias,  bishop  of  Rome, 

326 
Zahn,  Johannes,  76 
Zoroaster,  309 


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